Disable GitBranchCheck on commit presubmit

PRESUBMIT.py

 # Copyright (c) 2012 The Native Client Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Documentation on PRESUBMIT.py can be found at:
 # http://www.chromium.org/developers/how-tos/depottools/presubmit-scripts
 
 EXCLUDE_PROJECT_CHECKS_DIRS = [ '.' ]
 
 import subprocess
@@ skipping 18 matching lines @@
     return None
   print 'Warning: presubmit check could not determine local git branch'
   return None
 
 def _CommonChecks(input_api, output_api):
   """Checks for both upload and commit."""
   results = []
   results.extend(input_api.canned_checks.PanProjectChecks(
       input_api, output_api, project_name='Native Client',
       excluded_paths=tuple(EXCLUDE_PROJECT_CHECKS_DIRS)))
-  branch_warning = CheckGitBranch()
-  if branch_warning:
-    results.append(output_api.PresubmitPromptWarning(branch_warning))
   return results
 
 def CheckChangeOnUpload(input_api, output_api):
   """Verifies all changes in all files.
   Args:
     input_api: the limited set of input modules allowed in presubmit.
     output_api: the limited set of output modules allowed in presubmit.
   """
   report = []
   report.extend(_CommonChecks(input_api, output_api))
+  branch_warning = CheckGitBranch()
+  if branch_warning:
+    report.append(output_api.PresubmitPromptWarning(branch_warning))
   return report
 
 def CheckChangeOnCommit(input_api, output_api):
   """Verifies all changes in all files and verifies that the
   tree is open and can accept a commit.
   Args:
     input_api: the limited set of input modules allowed in presubmit.
     output_api: the limited set of output modules allowed in presubmit.
   """
   report = []
-  report.extend(CheckChangeOnUpload(input_api, output_api))
+  report.extend(_CommonChecks(input_api, output_api))
   return report
 
 def GetPreferredTrySlaves(project, change):
   return []