Fixes compilation on some versions of GCC and probably Clang.

Follow-up to http://crrev.com/c/786317

Bug: angleproject:1432
Change-Id: I3fc3ad0f65492f9543eb27fcdce6ca29a9ad06e5
Reviewed-on: https://chromium-review.googlesource.com/812220Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Kai Ninomiya <kainino@chromium.org>