Tests that sourcemap is applied correctly when specified by the respective HTTP header.

[expanded] 
element.style { ()

[expanded] 
#container #inspected { (selector-li…ader.scss:4 -> selector-line-sourcemap-header.scss:4:16)
    color: green;

[expanded] 
div { (user agent stylesheet)
    display: block;
    unicode-bidi: isolate;