MacViews: Implement event monitoring for a specific window (Reland)

ui/views/event_monitor_aura.h

 // 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.
 
 #ifndef UI_VIEWS_EVENT_MONITOR_AURA_H_
 #define UI_VIEWS_EVENT_MONITOR_AURA_H_
 
 #include "base/macros.h"
 #include "ui/views/event_monitor.h"
 
+namespace ui {
+class EventTarget;
+}
+
 namespace views {
 
 class EventMonitorAura : public EventMonitor {
  public:
-  explicit EventMonitorAura(ui::EventHandler* event_handler);
+  EventMonitorAura(ui::EventHandler* event_handler,
+                   ui::EventTarget* event_target);
   virtual ~EventMonitorAura();
 
  private:
   ui::EventHandler* event_handler_;  // Weak. Owned by our owner.
+  ui::EventTarget* event_target_;    // Weak.
 
   DISALLOW_COPY_AND_ASSIGN(EventMonitorAura);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_EVENT_MONITOR_AURA_H_