ui::GestureProvider gives GestureEventData the number of touch points.

ui/events/gesture_detection/gesture_event_data.cc

 // Copyright 2014 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 "ui/events/gesture_detection/gesture_event_data.h"
 
 #include "base/logging.h"
 
 namespace ui {
 
 GestureEventData::GestureEventData(EventType type,
                                    int motion_event_id,
                                    base::TimeTicks time,
                                    float x,
                                    float y,
+                                   int touch_point_count,
                                    const GestureEventDetails& details)
     : type(type),
       motion_event_id(motion_event_id),
       time(time),
       x(x),
       y(y),
       details(details) {
   DCHECK(motion_event_id >= 0);
+  DCHECK_NE(0, touch_point_count);
   DCHECK(ET_GESTURE_TYPE_START <= type && type <= ET_GESTURE_TYPE_END);
+  this->details.set_touch_points(touch_point_count);
 }
 
 GestureEventData::GestureEventData(EventType type,
                                    int motion_event_id,
                                    base::TimeTicks time,
                                    float x,
-                                   float y)
+                                   float y,
+                                   int touch_point_count)
     : type(type),
       motion_event_id(motion_event_id),
       time(time),
       x(x),
       y(y),
       details(GestureEventDetails(type, 0, 0)) {
   DCHECK(motion_event_id >= 0);
+  DCHECK_NE(0, touch_point_count);
   DCHECK(ET_GESTURE_TYPE_START <= type && type <= ET_GESTURE_TYPE_END);
+  details.set_touch_points(touch_point_count);
 }
 
 GestureEventData::GestureEventData() : type(ET_UNKNOWN), x(0), y(0) {}
 
 }  //  namespace ui