Fix crash in media::container_names::CheckMov.

      CheckMov didn't check for negative sizes sufficiently.

BUG=263073

Review URL: https://chromiumcodereview.appspot.com/21249003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@214875 0039d316-1c4b-4281-b951-d872f2087c98