Creating an ImageView for color Renderbuffers allows us to render to
them in a RenderPass. We will also need additional functionality to
support depth/stencil Renderbuffers.

Bug: angleproject:2347
Change-Id: I5d4f7d8242ad4fbca38cb08c0cf6b43edca57c8f
Reviewed-on: https://chromium-review.googlesource.com/922456
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Frank Henigman <fjhenigman@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>