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

ui/views/event_monitor_aura.h

Index: ui/views/event_monitor_aura.h
diff --git a/ui/views/event_monitor_aura.h b/ui/views/event_monitor_aura.h
index 21ff3bfffad14712b1a5bf5486fa5800e24de35c..d89ffc3f5e4fc75d8e507343b2aad19f6335e0cf 100644
--- a/ui/views/event_monitor_aura.h
+++ b/ui/views/event_monitor_aura.h
@@ -8,15 +8,21 @@
 #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);
 };