In some cases we would not validate the enums against the context version,
allowing the app to call through to unimplemented features.

BUG=angle:540

Change-Id: Ic89422a3a48882314c054f133961af0b4d8d739a
Reviewed-on: https://chromium-review.googlesource.com/180970Reviewed-by: Shannon Woods <shannonwoods@chromium.org>
Reviewed-by: Nicolas Capens <nicolascapens@chromium.org>
Commit-Queue: Nicolas Capens <nicolascapens@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>