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..48913b1c8e80e10813999156be1b862805740845
--- /dev/null
+++ b/ui/events/scoped_target_handler.h
@@ -0,0 +1,38 @@
+// 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/events_export.h"
+
+namespace ui {
+
+class EventHandler;
+class EventTarget;
+

[bruthig, 2015/11/19 16:49:53]

Some class level documentation would be useful here.

[varkha, 2015/11/19 23:34:35]

Done.

+class EVENTS_EXPORT ScopedTargetHandler {

[bruthig, 2015/11/19 16:49:53]

I envisioned that ScopedTargetHandler (or general subclasses of it) would extend
EventHandler and would set itself as the 'new' target handler, i.e.
set_target_handler(this).  This would allow us to push the
ToolbarButtonDelegate::On*Event() implementations up in to this more general
class. +1 for code re-use and less duplication once more InkDropDelegates are
born.

[varkha, 2015/11/19 23:34:35]

Done.

+ public:
+  ScopedTargetHandler(EventTarget* target, EventHandler* handler);
+  virtual ~ScopedTargetHandler();
+
+  EventHandler* original_target_handler() { return original_handler_; }
+
+ private:
+  // An EventTarget that is used to set and restore |original_handler_|.
+  EventTarget* target_;
+
+  // New handler that is set on |target_| for the lifetime of |this|.
+  EventHandler* handler_;
+
+  // 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_