GitLab

This will (1) make render tests perform pixel-wise
comparison and generate diff images, (2) allow you
to specify output directory for where to dump the
result images on the device, and (3) upload the results
to be visible from buildbot status page.

Review-Url: https://codereview.chromium.org/2866103002
Cr-Commit-Position: refs/heads/master@{#471144}