Add check to PRESUBMIT.py that local branch matches uploaded patch set
Add check to PRESUBMIT.py that local branch matches uploaded patch set

"git cl push" will push whatever is in the local branch instead
of using the patch in the Rietveld issue.
This presubmit check is to work around this behaviour.

R=mikelawther@chromium.org

Review URL: https://codereview.appspot.com/40650046

web-animations/web-animations-demos,dstockwell/web-animations-demos,dstockwell/web-animations-demos,robcolburn/web-animations-demos,samthor/web-animations-demos,web-animations/web-animations-demos,alancutter/web-animations-demos-old,robcolburn/web-animations-demos,samthor/web-animations-demos,robcolburn/web-animations-demos,samthor/web-animations-demos,web-animations/web-animations-demos,alancutter/web-animations-demos-old