Verify that UISourceCodes are removed as the frame gets navigated.


Running: dumpInitialWorkspace
Removed: 0 uiSourceCodes
Workspace: 2 uiSourceCodes.
    debugger:///VM[XXX]
    http://127.0.0.1:8000/devtools/resources/inspected-page.html

Running: attachFrame
Removed: 0 uiSourceCodes
Workspace: 8 uiSourceCodes.
    debugger:///VM[XXX]
[+] debugger:///VM[XXX] magic-script.js
[+] debugger:///VM[XXX] _test_attachFrame.js
[+] http://127.0.0.1:8000/devtools/bindings/resources/magic-frame.html
[+] http://127.0.0.1:8000/devtools/bindings/resources/magic-script.js
[+] http://127.0.0.1:8000/devtools/bindings/resources/magic-style.css
    http://127.0.0.1:8000/devtools/resources/inspected-page.html
[+] http://127.0.0.1:8000/devtools/resources/_test_attachFrame.js

Running: navigateFrame
Removed: 3 uiSourceCodes
[-] http://127.0.0.1:8000/devtools/bindings/resources/magic-frame.html
[-] http://127.0.0.1:8000/devtools/bindings/resources/magic-script.js
[-] http://127.0.0.1:8000/devtools/bindings/resources/magic-style.css
Workspace: 8 uiSourceCodes.
    debugger:///VM[XXX]
    debugger:///VM[XXX] magic-script.js
    debugger:///VM[XXX] _test_attachFrame.js
[+] debugger:///VM[XXX] _test_navigateFrame
[+] http://127.0.0.1:8000/devtools/bindings/resources/empty-frame.html
    http://127.0.0.1:8000/devtools/resources/inspected-page.html
    http://127.0.0.1:8000/devtools/resources/_test_attachFrame.js
[+] http://127.0.0.1:8000/devtools/resources/_test_navigateFrame