Refactoring to make adding ink drop animations easier

ui/events/scoped_target_handler.cc

Index: ui/events/scoped_target_handler.cc
diff --git a/ui/events/scoped_target_handler.cc b/ui/events/scoped_target_handler.cc
new file mode 100644
index 0000000000000000000000000000000000000000..bb39440a890572bdcadf6adf74408e0a6feb7550
--- /dev/null
+++ b/ui/events/scoped_target_handler.cc
@@ -0,0 +1,66 @@
+// Copyright 2015 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/scoped_target_handler.h"
+
+#include "ui/events/event.h"
+#include "ui/events/event_handler.h"
+#include "ui/events/event_target.h"
+
+namespace ui {
+
+ScopedTargetHandler::ScopedTargetHandler(EventTarget* target,
+                                         EventHandler* handler)
+    : destroyed_flag_(NULL), target_(target), new_handler_(handler){
+  original_handler_ = target_->SetTargetHandler(this);
+}
+
+ScopedTargetHandler::~ScopedTargetHandler() {
+  EventHandler* handler = target_->SetTargetHandler(original_handler_);
+  DCHECK_EQ(this, handler);
+  if (destroyed_flag_)
+    *destroyed_flag_ = true;
+}
+
+void ScopedTargetHandler::OnEvent(ui::Event* event) {
+  bool destroyed = false;
+  destroyed_flag_ = &destroyed;
+
+  if (original_handler_)
+    original_handler_->OnEvent(event);
+  else
+    EventHandler::OnEvent(event);
+
+  if (destroyed)
+    return;
+  destroyed_flag_ = NULL;
+
+  new_handler_->OnEvent(event);
+}
+
+void ScopedTargetHandler::OnKeyEvent(ui::KeyEvent* event) {
+  static_cast<EventHandler*>(target_)->OnKeyEvent(event);
+}
+
+void ScopedTargetHandler::OnMouseEvent(ui::MouseEvent* event) {
+  static_cast<EventHandler*>(target_)->OnMouseEvent(event);
+}
+
+void ScopedTargetHandler::OnScrollEvent(ui::ScrollEvent* event) {
+  static_cast<EventHandler*>(target_)->OnScrollEvent(event);
+}
+
+void ScopedTargetHandler::OnTouchEvent(ui::TouchEvent* event) {
+  static_cast<EventHandler*>(target_)->OnTouchEvent(event);
+}
+
+void ScopedTargetHandler::OnGestureEvent(ui::GestureEvent* event) {
+  static_cast<EventHandler*>(target_)->OnGestureEvent(event);
+}
+
+void ScopedTargetHandler::OnCancelMode(ui::CancelModeEvent* event) {
+  static_cast<EventHandler*>(target_)->OnCancelMode(event);
+}
+
+}  // namespace ui