This adds an internal and external version of the setShaderResource
method. The external version sets the state as dirty.

BUG=angleproject:2052

Change-Id: I6d2d47490c0af89ff5592d4e9c53eb69f8a3264d
Reviewed-on: https://chromium-review.googlesource.com/659397Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>