This method can allow the implementation to override the Context's
workarounds. Use this design pattern now that we have access to the
gl::Context everywhere - we don't need to cache a local copy in the
Renderer objects.

This will be used to apply a Shader Program Cache workaround on the
GL level, that will only be used for the GLES back-end on Qualcomm.

BUG=angleproject:2088

Change-Id: I6da25c5c29c3ba01b8820c5234d1b92dd2d2121a
Reviewed-on: https://chromium-review.googlesource.com/549980Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>