Mojo: Unify the disparate source and header files into 3

mojo/public/bindings/generators/cpp_templates/module_internal.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 $HEADER_GUARD
+
+#include "mojo/public/bindings/lib/bindings_serialization.h"
 #include "$HEADER"
 
-namespace $NAMESPACE {
-namespace internal {
-
-$IMPLEMENTATIONS
-
-}  // namespace internal
-}  // namespace sample
-
 namespace mojo {
 namespace internal {
 
-$SERIALIZATIONS
+$TRAITS
 
 }  // namespace internal
 }  // namespace mojo
+
+#endif  // $HEADER_GUARD