Passing this through the chain will allow us to have access to the
platform methods, as well as be useful in the future for Vulkan.

BUG=angleproject:1660

Change-Id: I819984fceeb5a2a299aa54e59ef3b428f5f9c91f
Reviewed-on: https://chromium-review.googlesource.com/438684Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>