Store the id of a contributing motion event in GestureEventData

ui/events/gesture_detection/scale_gesture_detector.h

 // 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.
 
 #ifndef UI_EVENTS_GESTURE_DETECTION_SCALE_GESTURE_DETECTOR_H_
 #define UI_EVENTS_GESTURE_DETECTION_SCALE_GESTURE_DETECTOR_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "base/time/time.h"
 #include "ui/events/gesture_detection/gesture_detection_export.h"
@@ skipping 14 matching lines @@
     ~Config();
     GestureDetector::Config gesture_detector_config;
     bool quick_scale_enabled;
     int min_scaling_touch_major;
     int min_scaling_span;
   };
 
   class ScaleGestureListener {
    public:
     virtual ~ScaleGestureListener() {}
-    virtual bool OnScale(const ScaleGestureDetector& detector) = 0;
-    virtual bool OnScaleBegin(const ScaleGestureDetector& detector) = 0;
-    virtual void OnScaleEnd(const ScaleGestureDetector& detector) = 0;
+    virtual bool OnScale(const ScaleGestureDetector& detector,
+                         const MotionEvent& e) = 0;
+    virtual bool OnScaleBegin(const ScaleGestureDetector& detector,
+                              const MotionEvent& e) = 0;
+    virtual void OnScaleEnd(const ScaleGestureDetector& detector,
+                            const MotionEvent& e) = 0;
   };
 
   // A convenience class to extend when you only want to listen for a subset of
   // scaling-related events. This implements all methods in
   // |ScaleGestureListener| but does nothing.
   // |OnScale()| returns false so that a subclass can retrieve the accumulated
   // scale factor in an overridden |OnScaleEnd()|.
   // |OnScaleBegin() returns true.
   class SimpleScaleGestureListener : public ScaleGestureListener {
    public:
     // ScaleGestureListener implementation.
-    virtual bool OnScale(const ScaleGestureDetector&) OVERRIDE;
-    virtual bool OnScaleBegin(const ScaleGestureDetector&) OVERRIDE;
-    virtual void OnScaleEnd(const ScaleGestureDetector&) OVERRIDE;
+    virtual bool OnScale(const ScaleGestureDetector&,
+                         const MotionEvent&) OVERRIDE;
+    virtual bool OnScaleBegin(const ScaleGestureDetector&,
+                              const MotionEvent&) OVERRIDE;
+    virtual void OnScaleEnd(const ScaleGestureDetector&,
+                            const MotionEvent&) OVERRIDE;
   };
 
   ScaleGestureDetector(const Config& config, ScaleGestureListener* listener);
   virtual ~ScaleGestureDetector();
 
   // Accepts MotionEvents and dispatches events to a |ScaleGestureListener|
   // when appropriate.
   //
   // Note: Applications should pass a complete and consistent event stream to
   // this method. A complete and consistent event stream involves all
@@ skipping 69 matching lines @@
   bool event_before_or_above_starting_gesture_event_;
 
   scoped_ptr<GestureDetector> gesture_detector_;
 
   DISALLOW_COPY_AND_ASSIGN(ScaleGestureDetector);
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_GESTURE_DETECTION_SCALE_GESTURE_DETECTOR_H_