Currently changing uniform values will not always be seen.

Bug: angleproject:2392
Bug: angleproject:2403
Change-Id: Ie315a64ad6094f2c23e48e901de2e03e4d98516a
Reviewed-on: https://chromium-review.googlesource.com/963296
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Luc Ferron <lucferron@chromium.org>