mash: Move ShelfWindowTargeter out of shelf_widget.cc

ash/shelf/shelf_window_targeter.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.
+
+#ifndef ASH_SHELF_SHELF_WINDOW_TARGETER_H_
+#define ASH_SHELF_SHELF_WINDOW_TARGETER_H_
+
+#include "ash/common/shelf/wm_shelf_observer.h"
+#include "ash/common/wm_window_observer.h"
+#include "base/macros.h"
+#include "ui/wm/core/easy_resize_window_targeter.h"
+
+namespace ash {
+
+class WmShelf;
+
+// ShelfWindowTargeter makes it easier to resize windows with the mouse when the
+// window-edge slightly overlaps with the shelf edge. The targeter also makes it
+// easier to drag the shelf out with touch while it is hidden.
+class ShelfWindowTargeter : public ::wm::EasyResizeWindowTargeter,
+                            public WmWindowObserver,
+                            public WmShelfObserver {
+ public:
+  ShelfWindowTargeter(WmWindow* container, WmShelf* shelf);
+  ~ShelfWindowTargeter() override;
+
+ private:
+  // WmWindowObserver:
+  void OnWindowDestroying(WmWindow* window) override;
+
+  // WmShelfObserver:
+  void WillChangeVisibilityState(ShelfVisibilityState new_state) override;
+
+  WmShelf* shelf_;
+
+  DISALLOW_COPY_AND_ASSIGN(ShelfWindowTargeter);
+};
+
+}  // namespace ash
+
+#endif  // ASH_SHELF_SHELF_WINDOW_TARGETER_H_