[New Multicolumn] Only the nearest ancestral flow thread may serve as a containing flow thread.

Source/core/layout/LayoutObject.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2004 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Google Inc. All rights reserved.
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 593 matching lines @@
     if (LayoutState* layoutState = view()->layoutState()) {
         if (LayoutFlowThread* flowThread = layoutState->flowThread())
             return flowThread;
     }
 
     // Not in the middle of layout so have to find the thread the slow way.
     LayoutObject* curr = const_cast<LayoutObject*>(this);
     while (curr) {
         if (curr->isLayoutFlowThread())
             return toLayoutFlowThread(curr);
-        curr = curr->containingBlock();
+        LayoutObject* containingBlock = curr->containingBlock();
+        curr = curr->parent();
+        while (curr != containingBlock) {
+            if (curr->isLayoutFlowThread()) {
+                // The nearest ancestor flow thread isn't in our containing block chain. Then we
+                // aren't really part of any flow thread, and we should stop looking. This happens
+                // when there are out-of-flow objects or column spanners.
+                return 0;

[dsinclair, 2015/04/27 14:45:24]

nit: nullptr

[mstensho (USE GERRIT), 2015/04/27 16:08:26]

Done.

Fixed the one a few lines below this one as well while I was at it.

+            }
+            curr = curr->parent();
+        }
     }
     return 0;
 }
 
 // FIXME: This could be used when changing the size of a renderer without children to skip some invalidations.
 // FIXME: This is incorrect for document element. Remove this when we enable slimming paint.
 static inline bool rendererHasNoBoxEffectObsolete(const LayoutObject& object)
 {
     return !object.style()->hasVisualOverflowingEffect() && !object.style()->hasBorder() && !object.style()->hasBackground();
 }
@@ skipping 1830 matching lines @@
     if (parent()->style()->visibility() != VISIBLE && style()->visibility() == VISIBLE && !hasLayer()) {
         if (!layer)
             layer = parent()->enclosingLayer();
         if (layer)
             layer->dirtyVisibleContentStatus();
     }
 
     if (!isFloating() && parent()->childrenInline())
         parent()->dirtyLinesFromChangedChild(this);
 
-    if (LayoutFlowThread* flowThread = parent()->flowThreadContainingBlock())
+    if (LayoutFlowThread* flowThread = flowThreadContainingBlock())
         flowThread->flowThreadDescendantWasInserted(this);
 }
 
 void LayoutObject::willBeRemovedFromTree()
 {
     // FIXME: We should ASSERT(isRooted()) but we have some out-of-order removals which would need to be fixed first.
 
     // If we remove a visible child from an invisible parent, we don't know the layer visibility any more.
     DeprecatedPaintLayer* layer = 0;
     if (parent()->style()->visibility() != VISIBLE && style()->visibility() == VISIBLE && !hasLayer()) {
@@ skipping 818 matching lines @@
 {
     if (object1) {
         const blink::LayoutObject* root = object1;
         while (root->parent())
             root = root->parent();
         root->showLayoutTreeAndMark(object1, "*", object2, "-", 0);
     }
 }
 
 #endif