third_party/protobuf: Update to HEAD (f52e188fe4)

third_party/protobuf/python/google/protobuf/message.py

 # Protocol Buffers - Google's data interchange format
 # Copyright 2008 Google Inc.  All rights reserved.
 # https://developers.google.com/protocol-buffers/
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 # notice, this list of conditions and the following disclaimer.
@@ skipping 207 matching lines @@
   # What do we do with fields that share names with Python keywords
   # like 'lambda' and 'yield'?
   #
   # nnorwitz says:
   # """
   # Typically (in python), an underscore is appended to names that are
   # keywords. So they would become lambda_ or yield_.
   # """
   def ListFields(self):
     """Returns a list of (FieldDescriptor, value) tuples for all
-    fields in the message which are not empty.  A singular field is non-empty
-    if HasField() would return true, and a repeated field is non-empty if
-    it contains at least one element.  The fields are ordered by field
-    number"""
+    fields in the message which are not empty.  A message field is
+    non-empty if HasField() would return true. A singular primitive field
+    is non-empty if HasField() would return true in proto2 or it is non zero
+    in proto3. A repeated field is non-empty if it contains at least one
+    element.  The fields are ordered by field number"""
     raise NotImplementedError
 
   def HasField(self, field_name):
     """Checks if a certain field is set for the message, or if any field inside
     a oneof group is set.  Note that if the field_name is not defined in the
     message descriptor, ValueError will be raised."""
     raise NotImplementedError
 
   def ClearField(self, field_name):
     """Clears the contents of a given field, or the field set inside a oneof
@@ skipping 44 matching lines @@
     raise NotImplementedError
 
   def __getstate__(self):
     """Support the pickle protocol."""
     return dict(serialized=self.SerializePartialToString())
 
   def __setstate__(self, state):
     """Support the pickle protocol."""
     self.__init__()
     self.ParseFromString(state['serialized'])