Disable mute/unmute when media does not have an audio track.

BUG=18970
TEST=test matrix videos ending in 0 should have mute context menu disabled

Review URL: http://codereview.chromium.org/174018

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@23889 0039d316-1c4b-4281-b951-d872f2087c98
4 files changed