Revert "Temporarily disabling CQ due to infrastructure problems."

This reverts commit 380884e0f09949b6c2dfa5954e74d9fb504d54cf since
the CQ-Rietveld integration is now supporting codereview.webrtc.org.

BUG=501332
TBR=phoglund@webrtc.org

Review URL: https://codereview.webrtc.org/1197713007.

Cr-Commit-Position: refs/heads/master@{#9475}
1 file changed