Use --force to reset a git repo before attempting to rebase during gclient sync/update

Patch Contributed By: Nasser Grainawi <nasser@codeaurora.org>

Review URL: http://codereview.chromium.org/548079

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@37020 0039d316-1c4b-4281-b951-d872f2087c98

gclient_scm.py

@@ -213,6 +213,8 @@ class GitWrapper(SCMWrapper, scm.GIT):
     self._Run(['remote', 'update'], redirect_stdout=False)
     files = self._Run(['diff', new_base, '--name-only']).split()
     file_list.extend([os.path.join(self.checkout_path, f) for f in files])
+    if options.force:
+      self._Run(['reset', '--hard', merge_base], redirect_stdout=False)
     self._Run(['rebase', '-v', '--onto', new_base, merge_base, cur_branch],
                 redirect_stdout=False, checkrc=False)