The CQ dry run feature was announced in https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/G5-X0_tfmok

The primary complain is that the presubmit builders fail because of OWNERS checks or because of "Missing LGTM from someone other than...".
This change skips those checks for dry runs.

BUG=chromium:477190

Review URL: https://codereview.chromium.org/1090943003

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@294853 0039d316-1c4b-4281-b951-d872f2087c98