Add querySurfacePointerANGLE method to Surface.

This method will more closely match the desktop GL implementation.

BUG=angle:795

Change-Id: I796b46bb6e8e895dad8d9824e8405edcc12e8a4f
Reviewed-on: https://chromium-review.googlesource.com/228915
Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>