git cl upload now diffs HEAD rather than working tree

BUG=179131
TEST=./tests/git_cl_test.py


Review URL: https://chromiumcodereview.appspot.com/12388027

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@185366 0039d316-1c4b-4281-b951-d872f2087c98
2 files changed