Get event targetting working for mouse events.

ui/events/event_target_iterator.h

Index: ui/events/event_target_iterator.h
diff --git a/ui/events/event_target_iterator.h b/ui/events/event_target_iterator.h
index 28b4a30202a3fa2e29d1f32520188f2ac5bb06cb..1333475a951a472eae5b27cd869b230102899b04 100644
--- a/ui/events/event_target_iterator.h
+++ b/ui/events/event_target_iterator.h
@@ -28,11 +28,11 @@ class EventTargetIteratorImpl : public EventTargetIterator {
       : begin_(children.rbegin()),
         end_(children.rend()) {
   }
-  virtual ~EventTargetIteratorImpl() {}
+  ~EventTargetIteratorImpl() override {}
 
-  virtual EventTarget* GetNextTarget() override {
+  EventTarget* GetNextTarget() override {
     if (begin_ == end_)
-      return NULL;
+      return nullptr;
     EventTarget* target = *(begin_);
     ++begin_;
     return target;
@@ -43,6 +43,31 @@ class EventTargetIteratorImpl : public EventTargetIterator {
   typename std::vector<T*>::const_reverse_iterator end_;
 };
 
+// Provides a version which keeps a copy of the data (for when it has to be
+// derived instead of pointed at).
+template <typename T>
+class CopyingEventTargetIteratorImpl : public EventTargetIterator {
+ public:
+  explicit CopyingEventTargetIteratorImpl(const std::vector<T*>& children)
+      : children_(children),
+        begin_(children_.rbegin()),
+        end_(children_.rend()) {}
+  ~CopyingEventTargetIteratorImpl() override {}
+
+  EventTarget* GetNextTarget() override {
+    if (begin_ == end_)
+      return nullptr;
+    EventTarget* target = *(begin_);
+    ++begin_;
+    return target;
+  }
+
+ private:
+  typename std::vector<T*> children_;
+  typename std::vector<T*>::const_reverse_iterator begin_;
+  typename std::vector<T*>::const_reverse_iterator end_;
+};
+
 }  // namespace ui
 
 #endif  // UI_EVENTS_EVENT_TARGET_ITERATOR_H_