Add new test cases to verify it properly handles "-1 +1, 2" and "-1 +1" for
short files.

R=petermayo@chromium.org
BUG=


Review URL: https://chromiumcodereview.appspot.com/10894036

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@153906 0039d316-1c4b-4281-b951-d872f2087c98