Better scrolling fix

third_party/WebKit/Source/core/paint/PaintLayer.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 279 matching lines @@
     {
         // FIXME: Remove incremental compositing updates after fixing the chicken/egg issues
         // https://code.google.com/p/chromium/issues/detail?id=343756
         DisableCompositingQueryAsserts disabler;
         updatePaginationRecursive(enclosingPaginationLayer());
     }
 }
 
 void PaintLayer::updateLayerPositionRecursive()
 {
+    if (m_scrollableArea)
+        m_scrollableArea->clampPositionAfterLayout();
+
     updateLayerPosition();
 
     if (m_rareData && m_rareData->reflectionInfo)
         m_rareData->reflectionInfo->reflection()->layout();
 
     // FIXME(400589): We would like to do this in PaintLayerScrollableArea::updateAfterLayout,
     // but it depends on the size computed by updateLayerPosition.
     if (m_scrollableArea) {
         if (ScrollAnimatorBase* scrollAnimator = m_scrollableArea->existingScrollAnimator())
             scrollAnimator->updateAfterLayout();
@@ skipping 2568 matching lines @@
 
 void showLayerTree(const blink::LayoutObject* layoutObject)
 {
     if (!layoutObject) {
         fprintf(stderr, "Cannot showLayerTree. Root is (nil)\n");
         return;
     }
     showLayerTree(layoutObject->enclosingLayer());
 }
 #endif