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

ui/events/event.cc

Index: ui/events/event.cc
diff --git a/ui/events/event.cc b/ui/events/event.cc
index 27de2a96b6a150891a4632df87890562f06a4eb0..13619d04569243039ce5a95cf81e8027f6748737 100644
--- a/ui/events/event.cc
+++ b/ui/events/event.cc
@@ -236,6 +236,10 @@ CancelModeEvent::CancelModeEvent()
 CancelModeEvent::~CancelModeEvent() {
 }
 
+scoped_ptr<Event> CancelModeEvent::Clone() const {
+  return scoped_ptr<Event>(new CancelModeEvent(*this));
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // LocatedEvent
 
@@ -269,6 +273,10 @@ void LocatedEvent::UpdateForRootTransform(
   root_location_ = location_;
 }
 
+scoped_ptr<Event> LocatedEvent::Clone() const {
+  return scoped_ptr<Event>(new LocatedEvent(*this));
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // MouseEvent
 
@@ -405,6 +413,10 @@ void MouseEvent::SetClickCount(int click_count) {
   set_flags(f);
 }
 
+scoped_ptr<Event> MouseEvent::Clone() const {
+  return scoped_ptr<Event>(new MouseEvent(*this));
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // MouseWheelEvent
 
@@ -463,6 +475,10 @@ void MouseWheelEvent::UpdateForRootTransform(
     offset_.set_y(offset_.y() * decomp.scale[1]);
 }
 
+scoped_ptr<Event> MouseWheelEvent::Clone() const {
+  return scoped_ptr<Event>(new MouseWheelEvent(*this));
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // TouchEvent
 
@@ -537,6 +553,10 @@ void TouchEvent::UpdateForRootTransform(
     radius_y_ *= decomp.scale[1];
 }
 
+scoped_ptr<Event> TouchEvent::Clone() const {
+  return scoped_ptr<Event>(new TouchEvent(*this));
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // KeyEvent
 
@@ -763,6 +783,10 @@ void KeyEvent::SetTranslated(bool translated) {
   }
 }
 
+scoped_ptr<Event> KeyEvent::Clone() const {
+  return scoped_ptr<Event>(new KeyEvent(*this));
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // ScrollEvent
 
@@ -811,6 +835,10 @@ void ScrollEvent::Scale(const float factor) {
   y_offset_ordinal_ *= factor;
 }
 
+scoped_ptr<Event> ScrollEvent::Clone() const {
+  return scoped_ptr<Event>(new ScrollEvent(*this));
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // GestureEvent
 
@@ -830,4 +858,8 @@ GestureEvent::GestureEvent(float x,
 GestureEvent::~GestureEvent() {
 }
 
+scoped_ptr<Event> GestureEvent::Clone() const {
+  return scoped_ptr<Event>(new GestureEvent(*this));
+}
+
 }  // namespace ui