[GCM] Add gcm_unit_tests to aura_builder target

BUG=284553

Review URL: https://codereview.chromium.org/136383004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246455 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246455