Add extra_headers to Rietveld.

It's needed to start a mapreduce on GAE with this class.

R=dpranke@chromium.org
BUG=
TEST=

Review URL: http://codereview.chromium.org/7076016

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@87010 0039d316-1c4b-4281-b951-d872f2087c98

rietveld.py

@@ -40,14 +40,15 @@ upload.logging.setLevel(logging.WARNING)  # pylint: disable=E1103
 
 class Rietveld(object):
   """Accesses rietveld."""
-  def __init__(self, url, email, password):
+  def __init__(self, url, email, password, extra_headers=None):
     self.issue = None
     self.url = url
     if email and password:
       get_creds = lambda: (email, password)
       self.rpc_server = upload.HttpRpcServer(
             self.url,
-            get_creds)
+            get_creds,
+            extra_headers=extra_headers)
     else:
       self.rpc_server = upload.GetRpcServer(url, email)
     self._xsrf_token = None