Indicate whether a touch event will cause scrolling

ui/events/gestures/gesture_recognizer.h

 // Copyright (c) 2012 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_GESTURES_GESTURE_RECOGNIZER_H_
 #define UI_EVENTS_GESTURES_GESTURE_RECOGNIZER_H_
 
 #include <vector>
 
 #include "base/memory/scoped_vector.h"
@@ skipping 11 matching lines @@
   static GestureRecognizer* Get();
   static void Reset();
 
   // List of GestureEvent*.
   typedef ScopedVector<GestureEvent> Gestures;
 
   virtual ~GestureRecognizer() {}
 
   // Invoked before event dispatch. If the event is invalid given the current
   // touch sequence, marks it as handled.
-  virtual bool ProcessTouchEventPreDispatch(const TouchEvent& event,
+  virtual bool ProcessTouchEventPreDispatch(TouchEvent* event,
                                             GestureConsumer* consumer) = 0;
   // Returns a list of zero or more GestureEvents. The caller is responsible for
   // freeing the returned events. Called synchronously after event dispatch.
   virtual Gestures* ProcessTouchEventPostDispatch(
       const TouchEvent& event,
       ui::EventResult result,
       GestureConsumer* consumer) = 0;
   // Returns a list of zero or more GestureEvents. The caller is responsible for
   // freeing the returned events. Called when a touch event receives an
   // asynchronous ack.
@@ skipping 50 matching lines @@
 
   // Unsubscribes |helper| from async gesture dispatch.
   // Since the GestureRecognizer does not own the |helper|, it is not deleted
   // and must be cleaned up appropriately by the caller.
   virtual void RemoveGestureEventHelper(GestureEventHelper* helper) = 0;
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_GESTURES_GESTURE_RECOGNIZER_H_