Non-composited, fixed position should trigger main thread scrolling

Source/core/rendering/RenderLayer.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 287 matching lines @@
         // in this case, there is no need to dirty our ancestors further.
         if (layer->isSelfPaintingLayer()) {
             ASSERT(!parent() || parent()->m_hasSelfPaintingLayerDescendantDirty || parent()->m_hasSelfPaintingLayerDescendant);
             break;
         }
     }
 }
 
 bool RenderLayer::scrollsWithViewport() const
 {
-    return renderer()->style()->position() == FixedPosition && renderer()->containingBlock()->enclosingLayer()->isRootLayer();
+    return renderer()->style()->position() == FixedPosition && renderer()->containerForFixedPosition() == renderer()->view();
 }
 
 bool RenderLayer::scrollsWithRespectTo(const RenderLayer* other) const
 {
     if (scrollsWithViewport() != other->scrollsWithViewport())
         return true;
     return ancestorScrollingLayer() != other->ancestorScrollingLayer();
 }
 
 void RenderLayer::updateTransformationMatrix()
@@ skipping 3367 matching lines @@
     }
 }
 
 void showLayerTree(const blink::RenderObject* renderer)
 {
     if (!renderer)
         return;
     showLayerTree(renderer->enclosingLayer());
 }
 #endif