Make top-layer elements work also when the viewport is paginated.

third_party/WebKit/Source/core/paint/PaintLayerStackingNode.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 25 matching lines @@
  * licenses (the MPL or the GPL) and not to allow others to use your
  * version of this file under the LGPL, indicate your decision by
  * deletingthe provisions above and replace them with the notice and
  * other provisions required by the MPL or the GPL, as the case may be.
  * If you do not delete the provisions above, a recipient may use your
  * version of this file under any of the LGPL, the MPL or the GPL.
  */
 
 #include "core/paint/PaintLayerStackingNode.h"
 
+#include "core/layout/LayoutMultiColumnFlowThread.h"
 #include "core/layout/LayoutView.h"
 #include "core/layout/compositing/PaintLayerCompositor.h"
 #include "core/paint/PaintLayer.h"
 #include "public/platform/Platform.h"
 #include <algorithm>
 
 namespace blink {
 
 // FIXME: This should not require PaintLayer. There is currently a cycle where
 // in order to determine if we isStacked() we have to ask the paint
@@ skipping 73 matching lines @@
     // Sort the two lists.
     if (m_posZOrderList)
         std::stable_sort(m_posZOrderList->begin(), m_posZOrderList->end(), compareZIndex);
 
     if (m_negZOrderList)
         std::stable_sort(m_negZOrderList->begin(), m_negZOrderList->end(), compareZIndex);
 
     // Append layers for top layer elements after normal layer collection, to ensure they are on top regardless of z-indexes.
     // The layoutObjects of top layer elements are children of the view, sorted in top layer stacking order.
     if (layer()->isRootLayer()) {
-        LayoutView* view = layoutObject()->view();
-        for (LayoutObject* child = view->firstChild(); child; child = child->nextSibling()) {
+        LayoutBlockFlow* rootBlock = layoutObject()->view();
+        // If the viewport is paginated, everything (including "top-layer" elements) gets
+        // redirected to the flow thread. So that's where we have to look, in that case.
+        if (LayoutBlockFlow* multiColumnFlowThread = rootBlock->multiColumnFlowThread())
+            rootBlock = multiColumnFlowThread;
+        for (LayoutObject* child = rootBlock->firstChild(); child; child = child->nextSibling()) {
             Element* childElement = (child->node() && child->node()->isElementNode()) ? toElement(child->node()) : 0;
             if (childElement && childElement->isInTopLayer()) {
                 PaintLayer* layer = toLayoutBoxModelObject(child)->layer();
                 // Create the buffer if it doesn't exist yet.
                 if (!m_posZOrderList)
                     m_posZOrderList = adoptPtr(new Vector<PaintLayerStackingNode*>);
                 m_posZOrderList->append(layer->stackingNode());
             }
         }
     }
@@ skipping 99 matching lines @@
     }
     return 0;
 }
 
 LayoutBoxModelObject* PaintLayerStackingNode::layoutObject() const
 {
     return m_layer->layoutObject();
 }
 
 } // namespace blink