This should fix our non-standard template use, which causes compile
errors for the tests on GCC/Clang.

BUG=angleproject:997

Change-Id: Id1bb15231eda445f37e53a5b33d4684ec6618d8e
Reviewed-on: https://chromium-review.googlesource.com/269858Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>