Fix git cl upload --squash (for Gerrit).
Fix git cl upload --squash (for Gerrit).

R=bauerb@chromium.org,andybons@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1590473002

git-svn-id: fd409f4bdeea2bb50a5d34bb4d4bfc2046a5a3dd@298270 0039d316-1c4b-4281-b951-d872f2087c98

primiano/depot_tools,primiano/depot_tools,CoherentLabs/depot_tools,CoherentLabs/depot_tools,primiano/depot_tools