Introduce SubjectBindingPointer. We can share the same pointer for the subject binding and the binding pointer. This further allows us to optimize buffer re-binding. The shared memory increases cache coherency and reduces the number of instructions needed. Bug: angleproject:2891 Change-Id: Id3162fa79de203f75989e7289ea02cb2ea1bec73 Reviewed-on: https://chromium-review.googlesource.com/c/1270217 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Frank Henigman <fjhenigman@chromium.org>