Break logic from VideoFrameStream into a generic templated DecoderStream.

BUG=347270

Review URL: https://codereview.chromium.org/130203003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253915 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253915