Add the member functions for saving and loading from the binary cache,
and hook them into the Program class. Requires that the Renderer
supports the program binary extension.

BUG=angleproject:1897

Change-Id: I2dc8d21b02da705ded58c5cd1943562c9c97c49b
Reviewed-on: https://chromium-review.googlesource.com/522874Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>