Some of these are targeting our workaround for a mac bug. The bug was
that the driver was somehow modifying output attachments that the
program wasn't writing to. A new test shows a bug where we wouldn't
re-sync the state properly after a clear.

Also adds more pretty printing for GLColor.

Bug: angleproject:2872
Change-Id: I5485893b5f1b269c5407678db27978a789f7acc6
Reviewed-on: https://chromium-review.googlesource.com/c/1269255
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>