Move SecurityOrigin::equals to SecurityOriginHash.

This method should only be used for hash comparisons; comparisons of
SecurityOrigin objects should use canAccess.

Review URL: https://codereview.chromium.org/36013004

git-svn-id: svn://svn.chromium.org/blink/trunk@164688 bbb929c8-8fbe-4397-9dbb-9b2b20218538