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

ui/events/event.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_H_
 #define UI_EVENTS_EVENT_H_
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/event_types.h"
@@ skipping 197 matching lines @@
   bool stopped_propagation() const { return !!(result_ & ER_CONSUMED); }
 
   // Marks the event as having been handled. A handled event does not reach the
   // next event phase. For example, if an event is handled during the pre-target
   // phase, then the event is dispatched to all pre-target handlers, but not to
   // the target or post-target handlers.
   // Note that SetHandled() can be called only for cancelable events.
   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);
   Event(const Event& copy);
   void SetType(EventType type);
   void set_delete_native_event(bool delete_native_event) {
     delete_native_event_ = delete_native_event;
   }
   void set_cancelable(bool cancelable) { cancelable_ = cancelable; }
 
@@ skipping 20 matching lines @@
 
   // The device id the event came from, or ED_UNKNOWN_DEVICE if the information
   // is not available.
   int source_device_id_;
 };
 
 class EVENTS_EXPORT CancelModeEvent : public Event {
  public:
   CancelModeEvent();
   virtual ~CancelModeEvent();
+
+  // Event:
+  virtual scoped_ptr<Event> Clone() const OVERRIDE;
 };
 
 class EVENTS_EXPORT LocatedEvent : public Event {
  public:
   virtual ~LocatedEvent();
 
   float x() const { return location_.x(); }
   float y() const { return location_.y(); }
   void set_location(const gfx::PointF& location) { location_ = location; }
   // TODO(tdresser): Always return floating point location. See
@@ skipping 19 matching lines @@
     if (!target || target == source)
       return;
     // TODO(tdresser): Rewrite ConvertPointToTarget to use PointF. See
     // crbug.com/337824.
     gfx::Point offset = gfx::ToFlooredPoint(location_);
     T::ConvertPointToTarget(source, target, &offset);
     gfx::Vector2d diff = gfx::ToFlooredPoint(location_) - offset;
     location_= location_ - diff;
   }
 
+  // Event:
+  virtual scoped_ptr<Event> Clone() const OVERRIDE;
+
  protected:
   friend class LocatedEventTestApi;
   explicit LocatedEvent(const base::NativeEvent& native_event);
 
   // Create a new LocatedEvent which is identical to the provided model.
   // If source / target windows are provided, the model location will be
   // converted from |source| coordinate system to |target| coordinate system.
   template <class T>
   LocatedEvent(const LocatedEvent& model, T* source, T* target)
       : Event(model),
@@ skipping 87 matching lines @@
   static bool IsRepeatedClickEvent(
       const MouseEvent& event1,
       const MouseEvent& event2);
 
   // Get the click count. Can be 1, 2 or 3 for mousedown messages, 0 otherwise.
   int GetClickCount() const;
 
   // 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.
   // NOTE: during a press and release flags() contains the complete set of
   // flags. Use this to determine the button that was pressed or released.
   int changed_button_flags() const { return changed_button_flags_; }
 
   // Updates the button that changed.
   void set_changed_button_flags(int flags) { changed_button_flags_ = flags; }
 
@@ skipping 49 matching lines @@
   // The amount to scroll. This is in multiples of kWheelDelta.
   // Note: x_offset() > 0/y_offset() > 0 means scroll left/up.
   int x_offset() const { return offset_.x(); }
   int y_offset() const { return offset_.y(); }
   const gfx::Vector2d& offset() const { return offset_; }
 
   // Overridden from LocatedEvent.
   virtual void UpdateForRootTransform(
       const gfx::Transform& inverted_root_transform) OVERRIDE;
 
+  // Event:
+  virtual scoped_ptr<Event> Clone() const OVERRIDE;
+
  private:
   gfx::Vector2d offset_;
 };
 
 class EVENTS_EXPORT TouchEvent : public LocatedEvent {
  public:
   explicit TouchEvent(const base::NativeEvent& native_event);
 
   // Create a new TouchEvent which is identical to the provided model.
   // If source / target windows are provided, the model location will be
@@ skipping 32 matching lines @@
   float force() const { return force_; }
 
   // Used for unit tests.
   void set_radius_x(const float r) { radius_x_ = r; }
   void set_radius_y(const float r) { radius_y_ = r; }
 
   // Overridden from 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;
     radius_y_ = radius_y;
   }
 
   void set_rotation_angle(float rotation_angle) {
     rotation_angle_ = rotation_angle;
   }
 
@@ skipping 122 matching lines @@
   // Normalizes flags_ so that it describes the state after the event.
   // (Native X11 event flags describe the state before the event.)
   void NormalizeFlags();
 
   // Returns true if the key event has already been processed by an input method
   // and there is no need to pass the key event to the input method again.
   bool IsTranslated() const;
   // 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;
 
   // This allows a subclass TranslatedKeyEvent to be a non character event.
   void set_is_char(bool is_char) { is_char_ = is_char; }
 
  private:
   KeyboardCode key_code_;
 
   // String of 'code' defined in DOM KeyboardEvent (e.g. 'KeyA', 'Space')
@@ skipping 53 matching lines @@
               float y_offset,
               float x_offset_ordinal,
               float y_offset_ordinal,
               int finger_count);
 
   // Scale the scroll event's offset value.
   // This is useful in the multi-monitor setup where it needs to be scaled
   // 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_; }
   float y_offset_ordinal() const { return y_offset_ordinal_; }
   int finger_count() const { return finger_count_; }
 
  private:
   // Potential accelerated offsets.
   float x_offset_;
   float y_offset_;
@@ skipping 16 matching lines @@
   // If source / target windows are provided, the model location will be
   // converted from |source| coordinate system to |target| coordinate system.
   template <typename T>
   GestureEvent(const GestureEvent& model, T* source, T* target)
       : LocatedEvent(model, source, target),
         details_(model.details_) {
   }
 
   virtual ~GestureEvent();
 
+  // Event:
+  virtual scoped_ptr<Event> Clone() const OVERRIDE;
+
   const GestureEventDetails& details() const { return details_; }
 
  private:
   GestureEventDetails details_;
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_EVENT_H_