Refactoring to make adding ink drop animations easier

ui/views/scoped_target_handler.h

+// 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.
+
+#ifndef UI_VIEWS_SCOPED_TARGET_HANDLER_H_
+#define UI_VIEWS_SCOPED_TARGET_HANDLER_H_
+
+#include "base/macros.h"
+#include "ui/events/event_handler.h"
+#include "ui/views/views_export.h"
+
+namespace views {
+
+class View;
+
+// An EventHandler that replaces an View's target handler with itself to pass
+// events first to the original handlers and second to an additional new
+// EventHandler. The new handler gets called after the original handlers even
+// if they call SetHandled() or StopPropagation() on the event.
+class VIEWS_EXPORT ScopedTargetHandler : public ui::EventHandler {
+ public:
+  ScopedTargetHandler(View* view, ui::EventHandler* new_handler);
+  ~ScopedTargetHandler() override;
+
+  // ui::EventHandler:
+  void OnEvent(ui::Event* event) override;
+  void OnKeyEvent(ui::KeyEvent* event) override;
+  void OnMouseEvent(ui::MouseEvent* event) override;
+  void OnScrollEvent(ui::ScrollEvent* event) override;
+  void OnTouchEvent(ui::TouchEvent* event) override;
+  void OnGestureEvent(ui::GestureEvent* event) override;
+  void OnCancelMode(ui::CancelModeEvent* event) override;
+
+ private:
+  // If non-null the destructor sets this to true. This is set while handling
+  // an event and used to detect if |this| has been deleted.
+  bool* destroyed_flag_;
+
+  // An View that has its target handler replaced with |this| for a life time of
+  // |this|.
+  View* view_;
+
+  // An EventHandler that gets restored on |view_| when |this| is destroyed.
+  ui::EventHandler* original_handler_;
+
+  // A new handler that gets events in addition to the |original_handler_| or
+  // |view_|.
+  ui::EventHandler* new_handler_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScopedTargetHandler);
+};
+
+}  // namespace views
+
+#endif  // UI_VIEWS_SCOPED_TARGET_HANDLER_H_