Add --upstream flag to presubmit_support for Git.
Add --upstream flag to presubmit_support for Git.

R=hinoka@chromium.org
BUG=368720

Review URL: https://codereview.chromium.org/267513002

git-svn-id: bd64dd6fa6f3f0ed0c0666d1018379882b742947@267254 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

svn2github/chromium-depot-tools,svn2github/chromium-depot-tools,svn2github/chromium-depot-tools