Introduced in https://chromium-review.googlesource.com/362641
Eventually we'll switch to using the same sets of warnings
for standalone and GN ANGLE.

BUG=angleproject:1441

Change-Id: I6534b9f85b952ddf1d953342cf9c8ddc5de6614e
Reviewed-on: https://chromium-review.googlesource.com/362780Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>