Fix CQ.cfg for Gerrit.

Follow up of https://codereview.chromium.org/2144723002.

BUG=627540
TBR=andybons@chromium.org

Review-Url: https://codereview.chromium.org/2139603004

infra/config/cq.cfg

@@ -4,6 +4,7 @@
 version: 1
 cq_name: "depot_tools"
 cq_status_url: "https://chromium-cq-status.appspot.com"
+git_repo_url: "https://chromium.googlesource.com/chromium/tools/depot_tools"
 
 gerrit {}
 rietveld {