Fix page jumping back to initial position after an overflow-bounce scroll.

Source/platform/mac/ScrollElasticityController.mm

 /*
  * 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 339 matching lines @@
                          roundToDevicePixelTowardZero(elasticDeltaForTimeDelta(m_startStretch.height(), -m_origVelocity.height(), (float)timeDelta)));
 
         if (fabs(delta.x()) >= 1 || fabs(delta.y()) >= 1) {
             m_client->immediateScrollByWithoutContentEdgeConstraints(FloatSize(delta.x(), delta.y()) - m_client->stretchAmount());
 
             FloatSize newStretch = m_client->stretchAmount();
 
             m_stretchScrollForce.setWidth(reboundDeltaForElasticDelta(newStretch.width()));
             m_stretchScrollForce.setHeight(reboundDeltaForElasticDelta(newStretch.height()));
         } else {
-            m_client->immediateScrollBy(m_origOrigin - m_client->absoluteScrollPosition());
+            m_client->adjustScrollPositionToBoundsIfNecessary();
 
             stopSnapRubberbandTimer();
             m_stretchScrollForce = FloatSize();
             m_startTime = 0;
             m_startStretch = FloatSize();
             m_origOrigin = FloatPoint();
             m_origVelocity = FloatSize();
         }
     } else {
         m_startTime = [NSDate timeIntervalSinceReferenceDate];
@@ skipping 48 matching lines @@
         return m_client->shouldRubberBandInDirection(ScrollLeft);
     if (wheelEvent.deltaX() < 0)
         return m_client->shouldRubberBandInDirection(ScrollRight);
 
     return true;
 }
 
 } // namespace WebCore
 
 #endif // USE(RUBBER_BANDING)