Update ScrollAnimator's copy of the layer dimensions after layout.

Source/core/layout/Layer.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 239 matching lines @@
     }
 }
 
 void Layer::updateLayerPositionRecursive()
 {
     updateLayerPosition();
 
     if (m_reflectionInfo)
         m_reflectionInfo->reflection()->layout();
 
+    // FIXME(400589): We would like to do this in RenderLayerScrollableArea::updateAfterLayout,
+    // but it depends on the size computed by updateLayerPosition.
+    if (m_scrollableArea) {
+        if (ScrollAnimator* scrollAnimator = m_scrollableArea->existingScrollAnimator())
+            scrollAnimator->updateAfterLayout();
+    }
+
     // FIXME: We should be able to remove this call because we don't care about
     // any descendant-dependent flags, but code somewhere else is reading these
     // flags and depending on us to update them.
     updateDescendantDependentFlags();
 
     for (Layer* child = firstChild(); child; child = child->nextSibling())
         child->updateLayerPositionRecursive();
 }
 
 void Layer::updateHasSelfPaintingLayerDescendant() const
@@ skipping 2659 matching lines @@
     }
 }
 
 void showLayerTree(const blink::LayoutObject* renderer)
 {
     if (!renderer)
         return;
     showLayerTree(renderer->enclosingLayer());
 }
 #endif