Do not mutate ui::Event properties during nested event processing

ui/events/event.h

Index: ui/events/event.h
diff --git a/ui/events/event.h b/ui/events/event.h
index 7257f625f40299b32510fb80850b4259db5f00c0..b55eeae84e563d70513e7fc725b03fa785fa51c8 100644
--- a/ui/events/event.h
+++ b/ui/events/event.h
@@ -215,6 +215,9 @@ class EVENTS_EXPORT Event {
   void SetHandled();
   bool handled() const { return result_ != ER_UNHANDLED; }
 
+  // Used to create a copy of |this|.
+  virtual scoped_ptr<Event> Clone() const = 0;

[sadrul, 2014/08/29 21:12:17]

Can we have a static Event::Clone(const Event& event); method that does the
right thing, e.g.:
  scoped_ptr<Event> Event::Clone(const Event& event) {
    if (event.IsMouseEvent())
      return scoped_ptr<Event>(new MouseEvent(cast<>(event)));
    ....

  }
etc.?

[tdanderson, 2014/09/02 22:57:09]

Done.

+
  protected:
   Event(EventType type, base::TimeDelta time_stamp, int flags);
   Event(const base::NativeEvent& native_event, EventType type, int flags);
@@ -255,6 +258,9 @@ class EVENTS_EXPORT CancelModeEvent : public Event {
  public:
   CancelModeEvent();
   virtual ~CancelModeEvent();
+
+  // Event:
+  virtual scoped_ptr<Event> Clone() const OVERRIDE;
 };
 
 class EVENTS_EXPORT LocatedEvent : public Event {
@@ -294,6 +300,9 @@ class EVENTS_EXPORT LocatedEvent : public Event {
     location_= location_ - diff;
   }
 
+  // Event:
+  virtual scoped_ptr<Event> Clone() const OVERRIDE;
+
  protected:
   friend class LocatedEventTestApi;
   explicit LocatedEvent(const base::NativeEvent& native_event);
@@ -401,6 +410,9 @@ class EVENTS_EXPORT MouseEvent : public LocatedEvent {
   // Set the click count for a mousedown message. Can be 1, 2 or 3.
   void SetClickCount(int click_count);
 
+  // Event:
+  virtual scoped_ptr<Event> Clone() const OVERRIDE;
+
   // Identifies the button that changed. During a press this corresponds to the
   // button that was pressed and during a release this corresponds to the button
   // that was released.
@@ -470,6 +482,9 @@ class EVENTS_EXPORT MouseWheelEvent : public MouseEvent {
   virtual void UpdateForRootTransform(
       const gfx::Transform& inverted_root_transform) OVERRIDE;
 
+  // Event:
+  virtual scoped_ptr<Event> Clone() const OVERRIDE;
+
  private:
   gfx::Vector2d offset_;
 };
@@ -522,6 +537,9 @@ class EVENTS_EXPORT TouchEvent : public LocatedEvent {
   virtual void UpdateForRootTransform(
       const gfx::Transform& inverted_root_transform) OVERRIDE;
 
+  // Event:
+  virtual scoped_ptr<Event> Clone() const OVERRIDE;
+
  protected:
   void set_radius(float radius_x, float radius_y) {
     radius_x_ = radius_x;
@@ -664,6 +682,9 @@ class EVENTS_EXPORT KeyEvent : public Event {
   // Marks this key event as translated or not translated.
   void SetTranslated(bool translated);
 
+  // Event:
+  virtual scoped_ptr<Event> Clone() const OVERRIDE;
+
  protected:
   friend class KeyEventTestApi;
 
@@ -737,6 +758,9 @@ class EVENTS_EXPORT ScrollEvent : public MouseEvent {
   // to provide a consistent user experience.
   void Scale(const float factor);
 
+  // Event:
+  virtual scoped_ptr<Event> Clone() const OVERRIDE;
+
   float x_offset() const { return x_offset_; }
   float y_offset() const { return y_offset_; }
   float x_offset_ordinal() const { return x_offset_ordinal_; }
@@ -773,6 +797,9 @@ class EVENTS_EXPORT GestureEvent : public LocatedEvent {
 
   virtual ~GestureEvent();
 
+  // Event:
+  virtual scoped_ptr<Event> Clone() const OVERRIDE;
+
   const GestureEventDetails& details() const { return details_; }
 
  private: