Add a MotionEventGeneric implementation

ui/events/gesture_detection/motion_event.h

Index: ui/events/gesture_detection/motion_event.h
diff --git a/ui/events/gesture_detection/motion_event.h b/ui/events/gesture_detection/motion_event.h
index b69a38f295abaf30ad2220f50a93ea8392066dcf..065f78e533ba77a05bda6730c120a6152ff578ea 100644
--- a/ui/events/gesture_detection/motion_event.h
+++ b/ui/events/gesture_detection/motion_event.h
@@ -57,19 +57,19 @@ class GESTURE_DETECTION_EXPORT MotionEvent {
   virtual float GetRawY(size_t pointer_index) const = 0;
   virtual float GetTouchMajor(size_t pointer_index) const = 0;
   virtual float GetPressure(size_t pointer_index) const = 0;
+  virtual ToolType GetToolType(size_t pointer_index) const = 0;
+  virtual int GetButtonState() const = 0;
   virtual base::TimeTicks GetEventTime() const = 0;
 
-  virtual size_t GetHistorySize() const = 0;
-  virtual base::TimeTicks GetHistoricalEventTime(
-      size_t historical_index) const = 0;
+  // Optional historical data, default implementation provides an empty history.
+  virtual size_t GetHistorySize() const;
+  virtual base::TimeTicks GetHistoricalEventTime(size_t historical_index) const;
   virtual float GetHistoricalTouchMajor(size_t pointer_index,
-                                        size_t historical_index) const = 0;
+                                        size_t historical_index) const;
   virtual float GetHistoricalX(size_t pointer_index,
-                               size_t historical_index) const = 0;
+                               size_t historical_index) const;
   virtual float GetHistoricalY(size_t pointer_index,
-                               size_t historical_index) const = 0;
-  virtual ToolType GetToolType(size_t pointer_index) const = 0;
-  virtual int GetButtonState() const = 0;
+                               size_t historical_index) const;
 
   virtual scoped_ptr<MotionEvent> Clone() const = 0;
   virtual scoped_ptr<MotionEvent> Cancel() const = 0;
@@ -85,6 +85,11 @@ class GESTURE_DETECTION_EXPORT MotionEvent {
   float GetPressure() const { return GetPressure(0); }
 };
 
+GESTURE_DETECTION_EXPORT bool operator==(const MotionEvent& lhs,
+                                         const MotionEvent& rhs);
+GESTURE_DETECTION_EXPORT bool operator!=(const MotionEvent& lhs,
+                                         const MotionEvent& rhs);
+
 }  // namespace ui
 
 #endif  // UI_EVENTS_GESTURE_DETECTION_MOTION_EVENT_H_