Remove mainthread overhang painting code

Source/core/paint/DeprecatedPaintLayerScrollableArea.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 477 matching lines @@
 int DeprecatedPaintLayerScrollableArea::visibleWidth() const
 {
     return layer()->size().width();
 }
 
 IntSize DeprecatedPaintLayerScrollableArea::contentsSize() const
 {
     return IntSize(scrollWidth(), scrollHeight());
 }
 
-IntSize DeprecatedPaintLayerScrollableArea::overhangAmount() const
-{
-    return IntSize();
-}
-
 IntPoint DeprecatedPaintLayerScrollableArea::lastKnownMousePosition() const
 {
     return box().frame() ? box().frame()->eventHandler().lastKnownMousePosition() : IntPoint();
 }
 
 bool DeprecatedPaintLayerScrollableArea::scrollAnimatorEnabled() const
 {
     if (Settings* settings = box().frame()->settings())
         return settings->scrollAnimatorEnabled();
     return false;
@@ skipping 879 matching lines @@
 void DeprecatedPaintLayerScrollableArea::setTopmostScrollChild(DeprecatedPaintLayer* scrollChild)
 {
     // We only want to track the topmost scroll child for scrollable areas with
     // overlay scrollbars.
     if (!hasOverlayScrollbars())
         return;
     m_nextTopmostScrollChild = scrollChild;
 }
 
 } // namespace blink