Support for '--force-compositing-mode', see WebKit bug 56156

BUG=
TEST=


Review URL: http://codereview.chromium.org/6665057

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@78904 0039d316-1c4b-4281-b951-d872f2087c98
6 files changed