This class logic will eventually move to the GL layer. Keep it
in the Renderer layer for now for refactoring purposes.

BUG=angleproject:1159

Change-Id: I91843099367f9a0293cc43ab98626bf79eb75ebf
Reviewed-on: https://chromium-review.googlesource.com/299875Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>