Add an interm ShaderSh class. 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/299875 Reviewed-by: Corentin Wallez <cwallez@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Tested-by: Jamie Madill <jmadill@chromium.org>