MacViews: Adds NativeWidgetMac and gets views target compiling on Mac.

ui/views/controls/native/native_view_host_mac.cc

+// Copyright 2014 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 "ui/views/controls/native/native_view_host_wrapper.h"
+
+namespace views {
+
+////////////////////////////////////////////////////////////////////////////////
+// NativeViewHostWrapper, public:
+
+// static
+NativeViewHostWrapper* NativeViewHostWrapper::CreateWrapper(
+    NativeViewHost* host) {
+  return NULL;
+}
+
+}  // namespace views