Mojo C++ bindings: add a new mode to generator to use native STL/WTF types

mojo/public/cpp/bindings/native_enum.h

 // Copyright 2016 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 MOJO_PUBLIC_CPP_BINDINGS_NATIVE_ENUM_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_NATIVE_ENUM_H_
 
+#include <functional>
+
+#include "mojo/public/cpp/bindings/lib/bindings_internal.h"
 #include "mojo/public/cpp/bindings/lib/native_enum_data.h"
 
 namespace mojo {
 
 // Native-only enums correspond to "[Native] enum Foo;" definitions in mojom.
 enum class NativeEnum : int32_t {};
 
 }  // namespace mojo
 
+namespace std {
+
+template <>
+struct hash<mojo::NativeEnum>
+    : public mojo::internal::EnumHashImpl<mojo::NativeEnum> {};
+
+}  // namespace std
+
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_NATIVE_ENUM_H_