ash: Refactor touch hud drawing to ash/touch_hud as a separate component.

ash/touch_hud/touch_hud_renderer.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_TOUCH_HUD_TOUCH_HUD_RENDERER_H_
+#define ASH_TOUCH_HUD_TOUCH_HUD_RENDERER_H_
+
+#include <map>
+#include <memory>
+
+#include "base/macros.h"
+
+namespace ui {
+class LocatedEvent;
+}
+
+namespace views {
+class Widget;
+}
+
+namespace ash {
+class TouchHudProjectionTest;
+class TouchPointView;
+
+// Handles touch events to draw out touch points accordingly.
+class TouchHudRenderer {
+ public:
+  TouchHudRenderer();
+  ~TouchHudRenderer();
+
+  // Called to clear touch points and traces from the screen.
+  void Clear();
+
+  // Receives a touch event and draws its touch point under parent_widget.
+  void HandleTouchEvent(const ui::LocatedEvent* event,
+                        views::Widget* parent_widget);

[sadrul, 2016/07/11 18:41:05]

Instead of sending the Widget here, can the Widget be sent along in the ctor
instead? Presumably, all the views created by this renderer should be in the
same widget?

[riajiang, 2016/07/11 20:39:34]

Changed to set parent_widget in the ctor.

+
+ private:
+  friend class TouchHudProjectionTest;
+
+  // a map of touch ids to TouchPointView
+  std::map<int, TouchPointView*> points_;
+
+  DISALLOW_COPY_AND_ASSIGN(TouchHudRenderer);
+};
+
+}  // namespace ash
+
+#endif  // ASH_TOUCH_HUD_TOUCH_HUD_RENDERER_H_