Do not assign revision when checking the commit existence.

checkout.py

 # coding=utf8
 # Copyright (c) 2012 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.
 """Manages a project checkout.
 
 Includes support for svn, git-svn and git.
 """
 
 import ConfigParser
@@ skipping 576 matching lines @@
       # Throw away all uncommitted changes in the existing checkout.
       self._check_call_git(['checkout', self.remote_branch])
       self._check_call_git(
           ['reset', '--hard', '--quiet',
            '%s/%s' % (self.remote, self.remote_branch)])
 
     if revision:
       try:
         # Look if the commit hash already exist. If so, we can skip a
         # 'git fetch' call.
-        revision = self._check_output_git(['rev-parse', revision])
+        revision = self._check_output_git(['rev-parse', revision]).rstrip()
       except subprocess.CalledProcessError:
         self._check_call_git(
             ['fetch', self.remote, self.remote_branch, '--quiet'])
-        revision = self._check_output_git(['rev-parse', revision])
+        revision = self._check_output_git(['rev-parse', revision]).rstrip()
       self._check_call_git(['checkout', '--force', '--quiet', revision])
     else:
       branches, active = self._branches()
       if active != self.master_branch:
         self._check_call_git(
             ['checkout', '--force', '--quiet', self.master_branch])
       self._sync_remote_branch()
 
       if self.working_branch in branches:
         self._call_git(['branch', '-D', self.working_branch])
@@ skipping 217 matching lines @@
   def revisions(self, rev1, rev2):
     return self.checkout.revisions(rev1, rev2)
 
   @property
   def project_name(self):
     return self.checkout.project_name
 
   @property
   def project_path(self):
     return self.checkout.project_path