Fix a typo in scm.GIT.GetBranch() and add --dry_run to trychange.py to ease testing.

scm.py

 # Copyright (c) 2006-2009 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """SCM-specific utility classes."""
 
 import os
 import re
 import shutil
 import subprocess
@@ skipping 70 matching lines @@
     return branch.replace('refs/heads/', '')
 
   @staticmethod
   def GetBranchRef(cwd):
     """Returns the full branch reference, e.g. 'refs/heads/master'."""
     return GIT.Capture(['symbolic-ref', 'HEAD'], cwd).strip()
 
   @staticmethod
   def GetBranch(cwd):
     """Returns the short branch name, e.g. 'master'."""
-    return GIT.ShortBranchName(GIT.BranchRef(cwd))
+    return GIT.ShortBranchName(GIT.GetBranchRef(cwd))
 
   @staticmethod
   def IsGitSvn(cwd):
     """Returns true if this repo looks like it's using git-svn."""
     # If you have any "svn-remote.*" config keys, we think you're using svn.
     try:
       GIT.Capture(['config', '--get-regexp', r'^svn-remote\.'], cwd)
       return True
     except gclient_utils.CheckCallError:
       return False
@@ skipping 558 matching lines @@
     if not cur_dir_repo_root:
       return None
 
     while True:
       parent = os.path.dirname(directory)
       if (SVN.CaptureInfo(parent, print_error=False).get(
               "Repository Root") != cur_dir_repo_root):
         break
       directory = parent
     return directory