Refactor ValidateMakeCurrent to pass egl object pointers instead of handles.

BUG=angleproject:2464

Change-Id: I98859f56d238a38bd6755f00dce7344635690491
Reviewed-on: https://chromium-review.googlesource.com/1053877
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Luc Ferron <lucferron@chromium.org>