Get event targetting working for mouse events.

ui/views/view.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_VIEWS_VIEW_H_
 #define UI_VIEWS_VIEW_H_
 
 #include <algorithm>
 #include <map>
 #include <set>
@@ skipping 698 matching lines @@
   // Returns the ViewTargeter installed on |this| if one exists,
   // otherwise returns the ViewTargeter installed on our root view.
   // The return value is guaranteed to be non-null.
   ViewTargeter* GetEffectiveViewTargeter() const;
 
   ViewTargeter* targeter() const { return targeter_.get(); }
 
   // Overridden from ui::EventTarget:
   bool CanAcceptEvent(const ui::Event& event) override;
   ui::EventTarget* GetParentTarget() override;
-  scoped_ptr<ui::EventTargetIterator> GetChildIterator() const override;
+  scoped_ptr<ui::EventTargetIterator> GetChildIterator() override;
   ui::EventTargeter* GetEventTargeter() override;
   void ConvertEventToTarget(ui::EventTarget* target,
                             ui::LocatedEvent* event) override;
 
   // Overridden from ui::EventHandler:
   void OnKeyEvent(ui::KeyEvent* event) override;
   void OnMouseEvent(ui::MouseEvent* event) override;
   void OnScrollEvent(ui::ScrollEvent* event) override;
   void OnTouchEvent(ui::TouchEvent* event) final;
   void OnGestureEvent(ui::GestureEvent* event) override;
@@ skipping 870 matching lines @@
   // Belongs to this view, but it's reference-counted on some platforms
   // so we can't use a scoped_ptr. It's dereferenced in the destructor.
   NativeViewAccessibility* native_view_accessibility_;
 
   DISALLOW_COPY_AND_ASSIGN(View);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_VIEW_H_