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

Source/platform/mac/ScrollAnimatorMac.mm

 /*
  * Copyright (C) 2010, 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 675 matching lines @@
 
     IntPoint minPos = m_scrollableArea->minimumScrollPosition();
     IntPoint maxPos = m_scrollableArea->maximumScrollPosition();
 
     float newX = max<float>(min<float>(position.x(), maxPos.x()), minPos.x());
     float newY = max<float>(min<float>(position.y(), maxPos.y()), minPos.y());
 
     return FloatPoint(newX, newY);
 }
 
+void ScrollAnimatorMac::adjustScrollPositionToBoundsIfNecessary()
+{
+    bool currentlyConstrainsToContentEdge = m_scrollableArea->constrainsScrollingToContentEdge();
+    m_scrollableArea->setConstrainsScrollingToContentEdge(true);
+
+    IntPoint currentScrollPosition = absoluteScrollPosition();
+    FloatPoint nearestPointWithinBounds = adjustScrollPositionIfNecessary(absoluteScrollPosition());
+    immediateScrollBy(nearestPointWithinBounds - currentScrollPosition);
+
+    m_scrollableArea->setConstrainsScrollingToContentEdge(currentlyConstrainsToContentEdge);
+}
+
 void ScrollAnimatorMac::immediateScrollTo(const FloatPoint& newPosition)
 {
     FloatPoint adjustedPosition = adjustScrollPositionIfNecessary(newPosition);
  
     bool positionChanged = adjustedPosition.x() != m_currentPosX || adjustedPosition.y() != m_currentPosY;
     if (!positionChanged && !scrollableArea()->scrollOriginChanged())
         return;
 
     FloatSize delta = FloatSize(adjustedPosition.x() - m_currentPosX, adjustedPosition.y() - m_currentPosY);
 
@@ skipping 578 matching lines @@
         return;
 
     m_visibleScrollerThumbRect = rectInViewCoordinates;
 }
 
 bool ScrollAnimatorMac::canUseCoordinatedScrollbar() {
     return isScrollbarOverlayAPIAvailable();
 }
 
 } // namespace WebCore