mus: Add PointerWatcher for passively observing mouse and touch events

ash/pointer_watcher_delegate_aura.h

+// Copyright 2016 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 "ash/ash_export.h"
+#include "ash/pointer_watcher_delegate.h"
+#include "base/macros.h"
+#include "base/observer_list.h"
+#include "ui/events/event_handler.h"
+
+namespace ash {
+
+// Support for PointerWatchers in non-mus ash, implemented with a pre-target
+// EventHandler on the Shell.
+class ASH_EXPORT PointerWatcherDelegateAura : public PointerWatcherDelegate,
+                                              public ui::EventHandler {
+ public:
+  PointerWatcherDelegateAura();
+  ~PointerWatcherDelegateAura() override;
+
+  // PointerWatcherDelegate:
+  void AddPointerWatcher(views::PointerWatcher* watcher) override;
+  void RemovePointerWatcher(views::PointerWatcher* watcher) override;
+
+  // ui::EventHandler:
+  void OnMouseEvent(ui::MouseEvent* event) override;
+  void OnTouchEvent(ui::TouchEvent* event) override;
+
+ private:
+  base::ObserverList<views::PointerWatcher> pointer_watchers_;
+
+  DISALLOW_COPY_AND_ASSIGN(PointerWatcherDelegateAura);
+};
+
+}  // namespace ash