Many of the members of SurfaceImpl could be stored in egl::Surface
instead.  This makes SurfaceImpl a pure interface and makes Surface
constructors much simpler.

BUG=angleproject:795

Change-Id: Ifa797b4bef84afe66f9fb3f3a6be260f726ca55c
Reviewed-on: https://chromium-review.googlesource.com/261358Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>