I've found it helpful and instructive to see what we're posting to
rietveld. Let's add it as a debug log for others too.  Can be helpful
to debug certain network issues.

Review URL: https://chromiumcodereview.appspot.com/11778015

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@175361 0039d316-1c4b-4281-b951-d872f2087c98