Mojo: Make MessageInTransit more opaque.

Still more to do, but incremental change is less scary.

R=yzshen@chromium.org

Review URL: https://codereview.chromium.org/172953003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252128 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 252128
The cricket::VideoCapturer no longer makes a copy of the frame from the camera. As a result we can't just do a shallow copy as the underlying buffer maybe invalid after the function returns. Instead we now have to make a copy in video_source_handler before return.

TEST=updated unit test
BUG=344957
R=perkj@chromium.org, wjia@chromium.org

Review URL: https://codereview.chromium.org/172843002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252129 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 252129