A div can be pan-scrolled beyond its overflow (Windows only)

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 2136 matching lines @@
     if (abs(delta.width()) <= ScrollView::noPanScrollRadius) // at the center we let the space for the icon
         delta.setWidth(0);
     if (abs(delta.height()) <= ScrollView::noPanScrollRadius)
         delta.setHeight(0);
 
     scrollByRecursively(adjustedScrollDelta(delta), ScrollOffsetClamped);
 }
 
 void RenderLayer::scrollByRecursively(const IntSize& delta, ScrollOffsetClamping clamp)
 {
+    scrollBy(delta, clamp, ShouldPropagateScroll);
+}
+
+bool RenderLayer::scrollBy(const IntSize& delta, ScrollOffsetClamping clamp, ScrollPropagation shouldPropagate)
+{
     if (delta.isZero())
-        return;
+        return false;
 
     bool restrictedByLineClamp = false;
     if (renderer()->parent())
         restrictedByLineClamp = !renderer()->parent()->style()->lineClamp().isNone();
 
     if (renderer()->hasOverflowClip() && !restrictedByLineClamp) {
         IntSize newScrollOffset = adjustedScrollOffset() + delta;
         scrollToOffset(newScrollOffset, clamp);
 
+        if (shouldPropagate == DontPropagateScroll)
+            return true;
+
         // If this layer can't do the scroll we ask the next layer up that can scroll to try
         IntSize remainingScrollOffset = newScrollOffset - adjustedScrollOffset();
+        bool didScroll = true;
         if (!remainingScrollOffset.isZero() && renderer()->parent()) {
             if (RenderLayer* scrollableLayer = enclosingScrollableLayer())
-                scrollableLayer->scrollByRecursively(remainingScrollOffset);
+                didScroll = scrollableLayer->scrollBy(remainingScrollOffset, clamp, shouldPropagate);
 
             Frame* frame = renderer()->frame();
             if (frame)
                 frame->eventHandler()->updateAutoscrollRenderer();
         }
+        return didScroll;
     } else if (renderer()->view()->frameView()) {
         // If we are here, we were called on a renderer that can be programmatically scrolled, but doesn't
         // have an overflow clip. Which means that it is a document node that can be scrolled.
-        renderer()->view()->frameView()->scrollBy(delta);
+        FrameView* view = renderer()->view()->frameView();
+        IntPoint scrollPositionBefore = view->scrollPosition();
+        if (view->isScrollable())
+            view->scrollBy(delta);
+        IntPoint scrollPositionAfter = view->scrollPosition();
+        return scrollPositionBefore != scrollPositionAfter;
 
         // FIXME: If we didn't scroll the whole way, do we want to try looking at the frames ownerElement? 
         // https://bugs.webkit.org/show_bug.cgi?id=28237
     }
+
+    return false;
 }
 
 IntSize RenderLayer::clampScrollOffset(const IntSize& scrollOffset) const
 {
     RenderBox* box = renderBox();
     ASSERT(box);
 
     int maxX = scrollWidth() - box->pixelSnappedClientWidth();
     int maxY = scrollHeight() - box->pixelSnappedClientHeight();
 
@@ skipping 4292 matching lines @@
     }
 }
 
 void showLayerTree(const WebCore::RenderObject* renderer)
 {
     if (!renderer)
         return;
     showLayerTree(renderer->enclosingLayer());
 }
 #endif