Reland r143115: Provide a Chrome-owned buffer to FFmpeg for video decoding (round 3).

      TEST=none
BUG=none
TBR=jam

Review URL: https://chromiumcodereview.appspot.com/10703018

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@144640 0039d316-1c4b-4281-b951-d872f2087c98