Avoid two targeting phases in aura client-lib and EventProcessor.

ui/aura/window_event_dispatcher.h

Index: ui/aura/window_event_dispatcher.h
diff --git a/ui/aura/window_event_dispatcher.h b/ui/aura/window_event_dispatcher.h
index 32b2b905bf04d5180ee83fdc869db514437a9ee5..eb2a3bb67506c0dda47b582417ccf5f4925387a4 100644
--- a/ui/aura/window_event_dispatcher.h
+++ b/ui/aura/window_event_dispatcher.h
@@ -60,6 +60,9 @@ class AURA_EXPORT WindowEventDispatcher : public ui::EventProcessor,
   Window* mouse_pressed_handler() { return mouse_pressed_handler_; }
   Window* mouse_moved_handler() { return mouse_moved_handler_; }
 
+  // Overridden from ui::EventProcessor:
+  ui::EventTargeter* GetDefaultEventTargeter() override;
+
   // Repost event for re-processing. Used when exiting context menus.
   // We support the ET_MOUSE_PRESSED, ET_TOUCH_PRESSED and ET_GESTURE_TAP_DOWN
   // event types (although the latter is currently a no-op).
@@ -173,7 +176,7 @@ class AURA_EXPORT WindowEventDispatcher : public ui::EventProcessor,
   void ReleaseNativeCapture() override;
 
   // Overridden from ui::EventProcessor:
-  ui::EventTarget* GetRootTarget() override;
+  ui::EventTarget* GetRootForEvent(ui::Event* event) override;
   void OnEventProcessingStarted(ui::Event* event) override;
   void OnEventProcessingFinished(ui::Event* event) override;
 
@@ -262,6 +265,9 @@ class AURA_EXPORT WindowEventDispatcher : public ui::EventProcessor,
 
   std::unique_ptr<MusMouseLocationUpdater> mus_mouse_location_updater_;
 
+  // The default EventTargeter for WindowEventDispatcher generated events.
+  std::unique_ptr<ui::EventTargeter> event_targeter_;
+
   // Used to schedule reposting an event.
   base::WeakPtrFactory<WindowEventDispatcher> repost_event_factory_;