This adds a commit queue for libyuv. The set of bots triggered
is the same as the set previously specified in PRESUBMIT.py. This
has two advantages over the current setup:
a) You get nice features in Gerrit (like a dry run button); and
b) You get a CQ!

Change-Id: I006e8480fa7238d9e7a0cfa0a932ddabcd71f511
Reviewed-on: https://chromium-review.googlesource.com/430917Reviewed-by: Frank Barchard <fbarchard@google.com>