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

ui/events/event_processor.h

Index: ui/events/event_processor.h
diff --git a/ui/events/event_processor.h b/ui/events/event_processor.h
index 8e6305148ba5d5dca5d8f3a1bdb03a6ac5a06038..6fffcc3fc870ca4c9b99cac754bbcec0f082c91a 100644
--- a/ui/events/event_processor.h
+++ b/ui/events/event_processor.h
@@ -14,7 +14,11 @@ namespace ui {
 // tree of EventTargets.
 class EVENTS_EXPORT EventProcessor : public EventDispatcherDelegate {
  public:
-  ~EventProcessor() override {}
+  ~EventProcessor() override;
+
+  void set_event_target(EventTarget* event_target) {
+    event_target_ = event_target;
+  }
 
   // Returns the root of the tree this event processor owns.
   virtual EventTarget* GetRootTarget() = 0;
@@ -42,6 +46,9 @@ class EVENTS_EXPORT EventProcessor : public EventDispatcherDelegate {
   // that the last target to which |event| was dispatched may have been
   // destroyed.
   virtual void OnEventProcessingFinished(Event* event);
+
+ private:
+  EventTarget* event_target_ = nullptr;
 };
 
 }  // namespace ui