GitLab

This patch enables audio / video thumbnail extraction. A lot of supporting code has already gone in. This is the last piece in the actual extension API that enables this.

BUG=304290

Review URL: https://codereview.chromium.org/250143002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@274849 0039d316-1c4b-4281-b951-d872f2087c98