Here it can be more easily accessed for command re-ordering, which
will use a RenderPass cache instead of having RenderPasses be owned
by the Framebuffer.

Bug: angleproject:2264
Change-Id: I9b06cff43e536a526d44e7e0c04027bc450051cf
Reviewed-on: https://chromium-review.googlesource.com/789533Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Frank Henigman <fjhenigman@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>