Includes fixes for some tests, and a new null platform class which
makes generating case lists easier.

BUG=angleproject:998

Change-Id: I1641c579bb63713fccde05e48f0cea31324f7d1b
Reviewed-on: https://chromium-review.googlesource.com/271202Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>