Debug video capture device to play back y4m movies.

For video quality and performance testing.


Based on a new command line flag:

--use-file-for-fake-video-capture=blabla.y4m

(Where blabla.y4m is the full path to the file to play)
This flag _must_ be used in combination with the existing:

--use-fake-device-for-media-stream

The file format can be found described in the code and also here:
http://wiki.multimedia.cx/index.php?title=YUV4MPEG2
And many examples here:
http://media.xiph.org/video/derf/
(Only 420 would work -- 422 is _not_ supported).

With these command line flag, navigating to a web site, f.e.
http://goo.gl/qdwf6, and allowing using the camera, will 
playback the video in a loop, as opposed to a fake camera or
a real camera stream.

BUG=318797

Review URL: https://codereview.chromium.org/61833011

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238973 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238973
<webview>: Mark loadplugin permission as stable

BUG=325798

Review URL: https://codereview.chromium.org/105143002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238974 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238974