Refactoring to make adding ink drop animations easier

ui/events/scoped_target_handler.h

Index: ui/events/scoped_target_handler.h
diff --git a/ui/events/scoped_target_handler.h b/ui/events/scoped_target_handler.h
new file mode 100644
index 0000000000000000000000000000000000000000..2552dfc86c55b98c312bcf57a82e478d37c6ec8c
--- /dev/null
+++ b/ui/events/scoped_target_handler.h
@@ -0,0 +1,45 @@
+// 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_EVENTS_SCOPED_TARGET_HANDLER_H_
+#define UI_EVENTS_SCOPED_TARGET_HANDLER_H_
+
+#include "base/macros.h"
+#include "ui/events/event_handler.h"
+#include "ui/events/events_export.h"
+
+namespace ui {
+
+class EventTarget;
+
+// An EventHandler that replaces an EventTarget's target handler with itself
+// to handle events on target or pass them to be handled in descendants.
+class EVENTS_EXPORT ScopedTargetHandler : public EventHandler {
+ public:
+  ScopedTargetHandler(EventTarget* target);

[bruthig, 2015/11/20 16:25:33]

I think the ScopedTargetHandler should still accept an EventHandler.  That way
it can be used by clients with a "has a" relationship instead of an "is a" one.
(And it would still work for "is a" relationships too)
Might be easiest to discuss offline.

[varkha, 2015/11/20 17:48:26]

Acknowledged.

[varkha, 2015/11/21 01:07:37]

Done.

+  ~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:
+  // An EventTarget that has its target handler replaced with |this| for a life
+  // time of |this|.
+  EventTarget* target_;
+
+  // An EventHandler that gets restored on |target_| when |this| is destroyed.
+  EventHandler* original_handler_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScopedTargetHandler);
+};
+
+}  // namespace ui
+
+#endif  // UI_EVENTS_SCOPED_TARGET_HANDLER_H_