Bump vendoring, move to proto3 release.

recipe_engine/third_party/google/protobuf/pyext/cpp_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 30 matching lines @@
 
 class GeneratedProtocolMessageType(_message.MessageMeta):
 
   """Metaclass for protocol message classes created at runtime from Descriptors.
 
   The protocol compiler currently uses this metaclass to create protocol
   message classes at runtime.  Clients can also manually create their own
   classes at runtime, as in this example:
 
   mydescriptor = Descriptor(.....)
-  class MyProtoClass(Message):
-    __metaclass__ = GeneratedProtocolMessageType
-    DESCRIPTOR = mydescriptor
+  factory = symbol_database.Default()
+  factory.pool.AddDescriptor(mydescriptor)
+  MyProtoClass = factory.GetPrototype(mydescriptor)
   myproto_instance = MyProtoClass()
   myproto.foo_field = 23
   ...
 
   The above example will not work for nested types. If you wish to include them,
   use reflection.MakeClass() instead of manually instantiating the class in
   order to create the appropriate class structure.
   """
 
   # Must be consistent with the protocol-compiler code in
   # proto2/compiler/internal/generator.*.
   _DESCRIPTOR_KEY = 'DESCRIPTOR'