Mojo: Unify the disparate source and header files into 3

mojo/public/bindings/generators/cpp_templates/struct_serialization.h-template

-// Copyright $YEAR 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.
-
-#ifndef $HEADER_GUARD
-#define $HEADER_GUARD
-
-#include "mojo/public/bindings/lib/bindings_serialization.h"
-
-namespace $NAMESPACE {
-class $CLASS;
-}
-
-namespace mojo {
-namespace internal {
-
-template <>
-class ObjectTraits<$FULL_CLASS> {
- public:
-  static size_t ComputeSizeOf(const $FULL_CLASS* $NAME);
-  static $FULL_CLASS* Clone(const $FULL_CLASS* bar, Buffer* buf);
-  static void EncodePointersAndHandles($FULL_CLASS* $NAME,
-                                       std::vector<mojo::Handle>* handles);
-  static bool DecodePointersAndHandles($FULL_CLASS* $NAME,
-                                       const mojo::Message& message);
-};
-
-}  // namespace internal
-}  // namespace mojo
-
-#endif  // $HEADER_GUARD