Refactoring to make adding ink drop animations easier

ui/events/event_target.h

 // 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.
 
 #ifndef UI_EVENTS_EVENT_TARGET_H_
 #define UI_EVENTS_EVENT_TARGET_H_
 
 #include <vector>
 
 #include "base/basictypes.h"
@@ skipping 59 matching lines @@
 
   // Adds a handler to receive events after the target. The handler must be
   // explicitly removed from the target before the handler is destroyed. The
   // EventTarget does not take ownership of the handler.
   void AddPostTargetHandler(EventHandler* handler);
   void RemovePostTargetHandler(EventHandler* handler);
 
   // Returns true if the event pre target list is empty.
   bool IsPreTargetListEmpty() const;
 
-  void set_target_handler(EventHandler* handler) {
-    target_handler_ = handler;
-  }
+  // Sets |target_handler| as |target_handler_| and returns its original value.
+  EventHandler* SetTargetHandler(EventHandler* target_handler);
 
  protected:
   EventHandler* target_handler() { return target_handler_; }
 
   // Overridden from EventHandler:
   void OnEvent(Event* event) override;
   void OnKeyEvent(KeyEvent* event) override;
   void OnMouseEvent(MouseEvent* event) override;
   void OnScrollEvent(ScrollEvent* event) override;
   void OnTouchEvent(TouchEvent* event) override;
@@ skipping 16 matching lines @@
   EventHandlerList pre_target_list_;
   EventHandlerList post_target_list_;
   EventHandler* target_handler_;
 
   DISALLOW_COPY_AND_ASSIGN(EventTarget);
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_EVENT_TARGET_H_