refactor presubmit parsing code from git-cl into presubmit

gcl.py

 #!/usr/bin/python
 # Copyright (c) 2010 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.
 
 """\
 Wrapper script around Rietveld's upload.py that simplifies working with groups
 of files.
 """
 
@@ skipping 1152 matching lines @@
   """Imports presubmit, then calls presubmit.DoPresubmitChecks."""
   # Need to import here to avoid circular dependency.
   import presubmit_support
   root_presubmit = GetCachedFile('PRESUBMIT.py', use_root=True)
   change = presubmit_support.SvnChange(change_info.name,
                                        change_info.description,
                                        change_info.GetLocalRoot(),
                                        change_info.GetFiles(),
                                        change_info.issue,
                                        change_info.patchset)
-  result = presubmit_support.DoPresubmitChecks(change=change,
+  output = presubmit_support.DoPresubmitChecks(change=change,
                                                committing=committing,
                                                verbose=False,
                                                output_stream=sys.stdout,
                                                input_stream=sys.stdin,
                                                default_presubmit=root_presubmit,
                                                may_prompt=may_prompt)
-  if not result and may_prompt:
+  if not output.should_continue() and may_prompt:
+    # TODO(dpranke): move into DoPresubmitChecks(), unify cmd line args.
     print "\nPresubmit errors, can't continue (use --no_presubmit to bypass)"
-  return result
+
+  # TODO(dpranke): Return the output object and make use of it.
+  return output.should_continue()
 
 
 @no_args
 def CMDchanges():
   """Lists all the changelists and their files."""
   for cl in GetCLs():
     change_info = ChangeInfo.Load(cl, GetRepositoryRoot(), True, True)
     print "\n--- Changelist " + change_info.name + ":"
     for filename in change_info.GetFiles():
       print "".join(filename)
@@ skipping 203 matching lines @@
     if e.code != 500:
       raise
     print >> sys.stderr, (
         'AppEngine is misbehaving and returned HTTP %d, again. Keep faith '
         'and retry or visit go/isgaeup.\n%s') % (e.code, str(e))
     return 1
 
 
 if __name__ == "__main__":
   sys.exit(main(sys.argv[1:]))