Broaden vp8 prefetch suppression to match new instances.

BUG=223255
TBR=zhaoqin@chromium.org

Review URL: https://codereview.chromium.org/132373004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248239 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 248239