There were a few calls that were using the context directly.
Consolidating them in the StateManager11 class should make efficient
state update after a Context switch possible. Also remove the Context
parameter from the setRenderTargets methods, since these are only
used internally and should be dirtying other states themselves.

BUG=angleproject:2052

Change-Id: I878c99fbde7a467f30cc89f2ee5aca476b8cf506
Reviewed-on: https://chromium-review.googlesource.com/659232Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>