This is a testharness.js-based test.
Found 112 FAIL, 0 TIMEOUT, 0 NOTRUN.
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [1 2 3 4] from add [1 2 3 4] to add [101 102 103 104] at (-0.25) should be [0]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [1 2 3 4] from add [1 2 3 4] to add [101 102 103 104] at (0) should be [2 4 6 8]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [1 2 3 4] from add [1 2 3 4] to add [101 102 103 104] at (0.25) should be [27 29 31 33]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [1 2 3 4] from add [1 2 3 4] to add [101 102 103 104] at (0.5) should be [52 54 56 58]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [1 2 3 4] from add [1 2 3 4] to add [101 102 103 104] at (0.75) should be [77 79 81 83]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [1 2 3 4] from add [1 2 3 4] to add [101 102 103 104] at (1) should be [102 104 106 108]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [1 2 3 4] from add [1 2 3 4] to add [101 102 103 104] at (1.25) should be [127 129 131 133]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [1 2 3 4] from add [1 2 3 4] to add [101 102 103 104] at (-0.25) should be [0]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [1 2 3 4] from add [1 2 3 4] to add [101 102 103 104] at (0) should be [2 4 6 8]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [1 2 3 4] from add [1 2 3 4] to add [101 102 103 104] at (0.25) should be [27 29 31 33]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [1 2 3 4] from add [1 2 3 4] to add [101 102 103 104] at (0.5) should be [52 54 56 58]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [1 2 3 4] from add [1 2 3 4] to add [101 102 103 104] at (0.75) should be [77 79 81 83]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [1 2 3 4] from add [1 2 3 4] to add [101 102 103 104] at (1) should be [102 104 106 108]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [1 2 3 4] from add [1 2 3 4] to add [101 102 103 104] at (1.25) should be [127 129 131 133]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [100 200 300 400] from add [100] to add [200 300 500] at (-0.25) should be [175 250 300 450]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [100 200 300 400] from add [100] to add [200 300 500] at (0) should be [200 300 400 500]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [100 200 300 400] from add [100] to add [200 300 500] at (0.25) should be [225 350 500 550]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [100 200 300 400] from add [100] to add [200 300 500] at (0.5) should be [250 400 600 600]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [100 200 300 400] from add [100] to add [200 300 500] at (0.75) should be [275 450 700 650]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [100 200 300 400] from add [100] to add [200 300 500] at (1) should be [300 500 800 700]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [100 200 300 400] from add [100] to add [200 300 500] at (1.25) should be [325 550 900 750]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [100 200 300 400] from add [100] to add [200 300 500] at (-0.25) should be [175 250 300 450]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [100 200 300 400] from add [100] to add [200 300 500] at (0) should be [200 300 400 500]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [100 200 300 400] from add [100] to add [200 300 500] at (0.25) should be [225 350 500 550]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [100 200 300 400] from add [100] to add [200 300 500] at (0.5) should be [250 400 600 600]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [100 200 300 400] from add [100] to add [200 300 500] at (0.75) should be [275 450 700 650]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [100 200 300 400] from add [100] to add [200 300 500] at (1) should be [300 500 800 700]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [100 200 300 400] from add [100] to add [200 300 500] at (1.25) should be [325 550 900 750]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [1 2 3px 4px] from add [1 2 3px 4px] to add [101 102 103px 104px] at (-0.25) should be [0 0 0px 0px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [1 2 3px 4px] from add [1 2 3px 4px] to add [101 102 103px 104px] at (0) should be [2 4 6px 8px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [1 2 3px 4px] from add [1 2 3px 4px] to add [101 102 103px 104px] at (0.25) should be [27 29 31px 33px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [1 2 3px 4px] from add [1 2 3px 4px] to add [101 102 103px 104px] at (0.5) should be [52 54 56px 58px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [1 2 3px 4px] from add [1 2 3px 4px] to add [101 102 103px 104px] at (0.75) should be [77 79 81px 83px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [1 2 3px 4px] from add [1 2 3px 4px] to add [101 102 103px 104px] at (1) should be [102 104 106px 108px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [1 2 3px 4px] from add [1 2 3px 4px] to add [101 102 103px 104px] at (1.25) should be [127 129 131px 133px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [1 2 3px 4px] from add [1 2 3px 4px] to add [101 102 103px 104px] at (-0.25) should be [0 0 0px 0px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [1 2 3px 4px] from add [1 2 3px 4px] to add [101 102 103px 104px] at (0) should be [2 4 6px 8px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [1 2 3px 4px] from add [1 2 3px 4px] to add [101 102 103px 104px] at (0.25) should be [27 29 31px 33px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [1 2 3px 4px] from add [1 2 3px 4px] to add [101 102 103px 104px] at (0.5) should be [52 54 56px 58px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [1 2 3px 4px] from add [1 2 3px 4px] to add [101 102 103px 104px] at (0.75) should be [77 79 81px 83px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [1 2 3px 4px] from add [1 2 3px 4px] to add [101 102 103px 104px] at (1) should be [102 104 106px 108px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [1 2 3px 4px] from add [1 2 3px 4px] to add [101 102 103px 104px] at (1.25) should be [127 129 131px 133px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [10px 20px] from add [190px 180px 290px 280px] to add [90px 80px] at (-0.25) should be [225px 225px 350px 350px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [10px 20px] from add [190px 180px 290px 280px] to add [90px 80px] at (0) should be [200px 200px 300px 300px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [10px 20px] from add [190px 180px 290px 280px] to add [90px 80px] at (0.25) should be [175px 175px 250px 250px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [10px 20px] from add [190px 180px 290px 280px] to add [90px 80px] at (0.5) should be [150px 150px 200px 200px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [10px 20px] from add [190px 180px 290px 280px] to add [90px 80px] at (0.75) should be [125px 125px 150px 150px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [10px 20px] from add [190px 180px 290px 280px] to add [90px 80px] at (1) should be [100px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [10px 20px] from add [190px 180px 290px 280px] to add [90px 80px] at (1.25) should be [75px 75px 50px 50px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [10px 20px] from add [190px 180px 290px 280px] to add [90px 80px] at (-0.25) should be [225px 225px 350px 350px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [10px 20px] from add [190px 180px 290px 280px] to add [90px 80px] at (0) should be [200px 200px 300px 300px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [10px 20px] from add [190px 180px 290px 280px] to add [90px 80px] at (0.25) should be [175px 175px 250px 250px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [10px 20px] from add [190px 180px 290px 280px] to add [90px 80px] at (0.5) should be [150px 150px 200px 200px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [10px 20px] from add [190px 180px 290px 280px] to add [90px 80px] at (0.75) should be [125px 125px 150px 150px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [10px 20px] from add [190px 180px 290px 280px] to add [90px 80px] at (1) should be [100px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [10px 20px] from add [190px 180px 290px 280px] to add [90px 80px] at (1.25) should be [75px 75px 50px 50px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [10 20px] from replace [100 100px] to add [190 180px] at (-0.25) should be [75 75px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [10 20px] from replace [100 100px] to add [190 180px] at (0) should be [100 100px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [10 20px] from replace [100 100px] to add [190 180px] at (0.25) should be [125 125px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [10 20px] from replace [100 100px] to add [190 180px] at (0.5) should be [150 150px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [10 20px] from replace [100 100px] to add [190 180px] at (0.75) should be [175 175px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [10 20px] from replace [100 100px] to add [190 180px] at (1) should be [200 200px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [10 20px] from replace [100 100px] to add [190 180px] at (1.25) should be [225 225px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [10 20px] from replace [100 100px] to add [190 180px] at (-0.25) should be [75 75px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [10 20px] from replace [100 100px] to add [190 180px] at (0) should be [100 100px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [10 20px] from replace [100 100px] to add [190 180px] at (0.25) should be [125 125px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [10 20px] from replace [100 100px] to add [190 180px] at (0.5) should be [150 150px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [10 20px] from replace [100 100px] to add [190 180px] at (0.75) should be [175 175px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [10 20px] from replace [100 100px] to add [190 180px] at (1) should be [200 200px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [10 20px] from replace [100 100px] to add [190 180px] at (1.25) should be [225 225px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [10px 20] from add [90px 80] to replace [0px 0 0px 0] at (-0.25) should be [125px 125]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [10px 20] from add [90px 80] to replace [0px 0 0px 0] at (0) should be [100px 100]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [10px 20] from add [90px 80] to replace [0px 0 0px 0] at (0.25) should be [75px 75]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [10px 20] from add [90px 80] to replace [0px 0 0px 0] at (0.5) should be [50px 50]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [10px 20] from add [90px 80] to replace [0px 0 0px 0] at (0.75) should be [25px 25]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [10px 20] from add [90px 80] to replace [0px 0 0px 0] at (1) should be [0px 0]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [10px 20] from add [90px 80] to replace [0px 0 0px 0] at (1.25) should be [0px 0]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [10px 20] from add [90px 80] to replace [0px 0 0px 0] at (-0.25) should be [125px 125]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [10px 20] from add [90px 80] to replace [0px 0 0px 0] at (0) should be [100px 100]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [10px 20] from add [90px 80] to replace [0px 0 0px 0] at (0.25) should be [75px 75]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [10px 20] from add [90px 80] to replace [0px 0 0px 0] at (0.5) should be [50px 50]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [10px 20] from add [90px 80] to replace [0px 0 0px 0] at (0.75) should be [25px 25]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [10px 20] from add [90px 80] to replace [0px 0 0px 0] at (1) should be [0px 0]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [10px 20] from add [90px 80] to replace [0px 0 0px 0] at (1.25) should be [0px 0]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [10 20] from add [100px 150px] to add [200px 250px] at (-0.25) should be [75px 125px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [10 20] from add [100px 150px] to add [200px 250px] at (0) should be [100px 150px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [10 20] from add [100px 150px] to add [200px 250px] at (0.25) should be [125px 175px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [10 20] from add [100px 150px] to add [200px 250px] at (0.5) should be [150px 200px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [10 20] from add [100px 150px] to add [200px 250px] at (0.75) should be [175px 225px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [10 20] from add [100px 150px] to add [200px 250px] at (1) should be [200px 250px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [10 20] from add [100px 150px] to add [200px 250px] at (1.25) should be [225px 275px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [10 20] from add [100px 150px] to add [200px 250px] at (-0.25) should be [75px 125px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [10 20] from add [100px 150px] to add [200px 250px] at (0) should be [100px 150px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [10 20] from add [100px 150px] to add [200px 250px] at (0.25) should be [125px 175px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [10 20] from add [100px 150px] to add [200px 250px] at (0.5) should be [150px 200px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [10 20] from add [100px 150px] to add [200px 250px] at (0.75) should be [175px 225px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [10 20] from add [100px 150px] to add [200px 250px] at (1) should be [200px 250px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [10 20] from add [100px 150px] to add [200px 250px] at (1.25) should be [225px 275px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [10 20] from add [100 150px] to add [200px 250] at (-0.25) should be [100 150px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [10 20] from add [100 150px] to add [200px 250] at (0) should be [100 150px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [10 20] from add [100 150px] to add [200px 250] at (0.25) should be [100 150px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [10 20] from add [100 150px] to add [200px 250] at (0.5) should be [200px 250]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [10 20] from add [100 150px] to add [200px 250] at (0.75) should be [200px 250]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [10 20] from add [100 150px] to add [200px 250] at (1) should be [200px 250]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing CSS Animations: property <mask-border-outset> underlying [10 20] from add [100 150px] to add [200px 250] at (1.25) should be [200px 250]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [10 20] from add [100 150px] to add [200px 250] at (-0.25) should be [100 150px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [10 20] from add [100 150px] to add [200px 250] at (0) should be [100 150px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [10 20] from add [100 150px] to add [200px 250] at (0.25) should be [100 150px]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [10 20] from add [100 150px] to add [200px 250] at (0.5) should be [200px 250]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [10 20] from add [100 150px] to add [200px 250] at (0.75) should be [200px 250]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [10 20] from add [100 150px] to add [200px 250] at (1) should be [200px 250]
  assert_true: 'from' value should be supported expected true got false
[FAIL] Compositing Web Animations: property <mask-border-outset> underlying [10 20] from add [100 150px] to add [200px 250] at (1.25) should be [200px 250]
  assert_true: 'from' value should be supported expected true got false
Harness: the test ran to completion.