Enable drawingbuffer tests on mac intel.

It seems they no longer hang the WindorServer.

BUG=303915
TEST=mac gpu intel bots
TBR=kbr@chromium.org

Review URL: https://codereview.chromium.org/166323016

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252357 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 252357