Add bounds validation to AsyncPixelTransfersCompletedQuery::End

BUG=351852
R=jbauman@chromium.org, jorgelo@chromium.org

Review URL: https://codereview.chromium.org/198253002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@256723 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 256723