Moves around mojo js bindings code

mojo/apps/js/bindings/handle.h

-// Copyright 2013 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_APPS_JS_BINDINGS_HANDLE_H_
-#define MOJO_APPS_JS_BINDINGS_HANDLE_H_
-
-#include "gin/converter.h"
-#include "mojo/public/system/core_cpp.h"
-
-namespace gin {
-
-template<>
-struct Converter<mojo::Handle> {
-  static v8::Handle<v8::Value> ToV8(v8::Isolate* isolate,
-                                    const mojo::Handle& val);
-  static bool FromV8(v8::Isolate* isolate, v8::Handle<v8::Value> val,
-                     mojo::Handle* out);
-};
-
-}  // namespace gin
-
-#endif  // MOJO_APPS_JS_BINDINGS_HANDLE_H_