Refactor CopyNativeEvent and add events_mac.mm to start implementing stubs

ui/events/events_stub.cc

 // Copyright (c) 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.
 
 #include "base/logging.h"
 #include "base/time/time.h"
 #include "build/build_config.h"
 #include "ui/events/event_utils.h"
 #include "ui/gfx/point.h"
 #include "ui/gfx/vector2d.h"
@@ skipping 44 matching lines @@
     const base::NativeEvent& native_event) {
   NOTIMPLEMENTED();
   return 0;
 }
 
 gfx::Vector2d GetMouseWheelOffset(const base::NativeEvent& native_event) {
   NOTIMPLEMENTED();
   return gfx::Vector2d();
 }
 
+base::NativeEvent CopyNativeEvent(const base::NativeEvent& event) {
+  NOTREACHED() << "Don't know how to copy base::NativeEvent for this platform";
+  return NULL;
+}
+
+void ReleaseCopiedNativeEvent(const base::NativeEvent& event) {}
+
 void ClearTouchIdIfReleased(const base::NativeEvent& native_event) {
   NOTIMPLEMENTED();
 }
 
 int GetTouchId(const base::NativeEvent& native_event) {
   NOTIMPLEMENTED();
   return 0;
 }
 
 float GetTouchRadiusX(const base::NativeEvent& native_event) {
@@ skipping 61 matching lines @@
   NOTIMPLEMENTED();
   return static_cast<KeyboardCode>(0);
 }
 
 const char* CodeFromNative(const base::NativeEvent& native_event) {
   NOTIMPLEMENTED();
   return "";
 }
 
 }  // namespace ui