Refactor screen/monitor so that gfx::Screen returns monitor object.

ui/aura/monitor_observer.cc

Index: ui/aura/monitor_observer.cc
diff --git a/ui/aura/monitor_observer.cc b/ui/aura/monitor_observer.cc
new file mode 100644
index 0000000000000000000000000000000000000000..aa1cf0f415cd441d2eda5c49825f4cadd8142620
--- /dev/null
+++ b/ui/aura/monitor_observer.cc
@@ -0,0 +1,12 @@
+// Copyright (c) 2012 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/aura/monitor_observer.h"
+
+namespace aura {
+
+MonitorObserver::~MonitorObserver() {
+}
+
+}  // namespace aura