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

ui/events/event.cc

 // 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.
 
 #include "ui/events/event.h"
 
 #if defined(USE_X11)
 #include <X11/extensions/XInput2.h>
 #include <X11/Xlib.h>
 #endif
@@ skipping 93 matching lines @@
 #endif
 }
 
 }  // namespace
 
 namespace ui {
 
 ////////////////////////////////////////////////////////////////////////////////
 // Event
 
+// static
+scoped_ptr<Event> Event::Clone(const Event& event) {
+  if (event.IsKeyEvent()) {
+    return scoped_ptr<Event>(new KeyEvent(static_cast<const KeyEvent&>(event)));
+  }
+
+  if (event.IsMouseEvent()) {
+    if (event.IsMouseWheelEvent()) {
+      return scoped_ptr<Event>(
+          new MouseWheelEvent(static_cast<const MouseWheelEvent&>(event)));
+    }
+
+    return scoped_ptr<Event>(
+        new MouseEvent(static_cast<const MouseEvent&>(event)));
+  }
+
+  if (event.IsTouchEvent()) {
+    return scoped_ptr<Event>(
+        new TouchEvent(static_cast<const TouchEvent&>(event)));
+  }
+
+  if (event.IsGestureEvent()) {
+    return scoped_ptr<Event>(
+        new GestureEvent(static_cast<const GestureEvent&>(event)));
+  }
+
+  if (event.IsScrollEvent()) {
+    return scoped_ptr<Event>(
+        new ScrollEvent(static_cast<const ScrollEvent&>(event)));
+  }
+
+  return scoped_ptr<Event>(new Event(event));
+}
+
 Event::~Event() {
   if (delete_native_event_)
     ReleaseCopiedNativeEvent(native_event_);
 }
 
 GestureEvent* Event::AsGestureEvent() {
   CHECK(IsGestureEvent());
   return static_cast<GestureEvent*>(this);
 }
 
@@ skipping 700 matching lines @@
                    gfx::PointF(x, y),
                    time_stamp,
                    flags | EF_FROM_TOUCH),
       details_(details) {
 }
 
 GestureEvent::~GestureEvent() {
 }
 
 }  // namespace ui