Fix stubbornly invalid comboboxes (that don't reset when selecting "New X...").

R=estade@chromium.org
BUG=313026
TEST=browser_tests, manual (see bug)

Review URL: https://codereview.chromium.org/59713007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@233669 0039d316-1c4b-4281-b951-d872f2087c98
Re-land https://codereview.chromium.org/56713002/ with ChromeOS fix.

Remove RGB32 from VideoFrame::Format.

It wasn't used anywhere outside of the unit tests.

BUG=313827
TBR=danakj

Review URL: https://codereview.chromium.org/60573005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@233670 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 233670