ash: Add basic prediction code to the laser pointer.

ash/laser/laser_pointer_points.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_LASER_LASER_POINTER_POINTS_H_
 #define ASH_LASER_LASER_POINTER_POINTS_H_
 
 #include <deque>
 #include <memory>
 
 #include "ash/ash_export.h"
 #include "base/macros.h"
 #include "base/time/time.h"
 #include "ui/gfx/geometry/point_f.h"
 #include "ui/gfx/geometry/rect.h"
 
 namespace ash {
 
 // LaserPointerPoints is a helper class used for displaying the palette tool
 // laser pointer. It keeps track of the points needed to render the laser
 // pointer and its tail.
 class ASH_EXPORT LaserPointerPoints {
  public:
   // Struct to describe each point.
   struct LaserPoint {
     gfx::PointF location;
+    base::TimeTicks time;
     // age is a value between [0,1] where 0 means the point was just added and 1
     // means that the point is just about to be removed.
     float age = 0.0f;
   };
 
   // Constructor with a parameter to choose the fade out time of the points in
   // the collection.
   explicit LaserPointerPoints(base::TimeDelta life_duration);
   ~LaserPointerPoints();
 
   // Adds a point. Automatically clears points that are too old.
-  void AddPoint(const gfx::PointF& point);
+  void AddPoint(const gfx::PointF& point, const base::TimeTicks& time);
   // Updates the collection latest time. Automatically clears points that are
   // too old.
-  void MoveForwardToTime(const base::Time& latest_time);
+  void MoveForwardToTime(const base::TimeTicks& latest_time);
   // Removes all points.
   void Clear();
   // Gets the bounding box of the points.
   gfx::Rect GetBoundingBox();
   // Returns the oldest point in the collection.
   LaserPoint GetOldest() const;
   // Returns the newest point in the collection.
   LaserPoint GetNewest() const;
   // Returns the number of points in the collection.
   int GetNumberOfPoints() const;
   // Whether there are any points or not.
   bool IsEmpty() const;
   // Expose the collection so callers can work with the points.
-  const std::deque<LaserPoint>& laser_points();
+  const std::deque<LaserPoint>& laser_points() const;
 
  private:
   friend class LaserPointerPointsTestApi;
 
   base::TimeDelta life_duration_;
   std::deque<LaserPoint> points_;
   // The latest time of the collection of points. This gets updated when new
   // points are added or when MoveForwardInTime is called.
-  base::Time collection_latest_time_;
+  base::TimeTicks collection_latest_time_;
 
   DISALLOW_COPY_AND_ASSIGN(LaserPointerPoints);
 };
 
 }  // namespace ash
 
 #endif  // ASH_LASER_LASER_POINTER_POINTS_H_