This helper allows us to quickly iterate state bits from the
Impl/Renderer layers.

Re-land with no C++11 usage.

BUG=angleproject:1040
TEST=angle_unittests (Mac/Win/Linux)

Change-Id: I3b6d5beb2bcff7fa3d45c9220d7c026c64c45d2e
Reviewed-on: https://chromium-review.googlesource.com/290153Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>