Remove touch scroll chaining from main thread scrolling.

Source/platform/PlatformGestureEvent.h

 /*
  * Copyright (C) 2011 Apple Inc.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 104 matching lines @@
     }
 
     bool inertial() const
     {
         ASSERT(m_type == PlatformEvent::GestureScrollUpdate || m_type == PlatformEvent::GestureScrollEnd);
         return m_data.m_scroll.m_inertial;
     }
 
     bool preventPropagation() const
     {
+        // TODO(tdresser) Once we've decided if we're getting rid of scroll
+        // chaining, we should remove all scroll chaining related logic. See
+        // crbug.com/526462 for details.
         ASSERT(m_type == PlatformEvent::GestureScrollUpdate);
-        return m_data.m_scroll.m_preventPropagation;
+        return true;
     }
 
     float scale() const
     {
         ASSERT(m_type == PlatformEvent::GesturePinchUpdate);
         return m_data.m_pinchUpdate.m_scale;
     }
 
     void applyTouchAdjustment(const IntPoint& adjustedPosition)
     {
@@ skipping 52 matching lines @@
 
         struct {
             float m_scale;
         } m_pinchUpdate;
     } m_data;
 };
 
 } // namespace blink
 
 #endif // PlatformGestureEvent_h