Video track clone cannot preserve original property

Video track clone cannot preserve original property
https://bugs.webkit.org/show_bug.cgi?id=189872
<rdar://problem/44706579>

Patch by YUHAN WU <yuhan_wu@apple.com> on 2018-09-26
Reviewed by Youenn Fablet.

LayoutTests/imported/w3c:

* web-platform-tests/mst-content-hint/MediaStreamTrack-contentHint-expected.txt:

Source/WebCore:

Fix the issue that the cloned track created by canvas.captureStream().getVideoTracks() cannot keep some attributes, such as enabled.
Updated a testcase expected result:
LayoutTests/imported/w3c/web-platform-tests/mst-content-hint/MediaStreamTrack-contentHint.html

* Modules/mediastream/CanvasCaptureMediaStreamTrack.cpp:
(WebCore::CanvasCaptureMediaStreamTrack::CanvasCaptureMediaStreamTrack):
(WebCore::CanvasCaptureMediaStreamTrack::create):
(WebCore::CanvasCaptureMediaStreamTrack::clone):
* Modules/mediastream/CanvasCaptureMediaStreamTrack.h:
* Modules/mediastream/MediaStreamTrack.h:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@236536 268f45cc-cd09-0410-ab3c-d52691b4dbfc