Add mocks of TextureImpl and RenderbufferImpl. BUG=angleproject:970 Change-Id: I63a7d8363f90018827c5d8482c9d98f3fa61c573 Reviewed-on: https://chromium-review.googlesource.com/286553 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org> Tested-by: Geoff Lang <geofflang@chromium.org>