Move code for locating the containing flow thread out of LayoutObject.

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 651 matching lines @@
 {
     ASSERT(isInsideFlowThread());
 
     // See if we have the thread cached because we're in the middle of layout.
     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->isSVG() && !curr->isSVGRoot())
-            return nullptr;
-        if (curr->isLayoutFlowThread())
-            return toLayoutFlowThread(curr);
-        LayoutObject* container = curr->container();
-        curr = curr->parent();
-        while (curr != container) {
-            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 nullptr;
-            }
-            curr = curr->parent();
-        }
-    }
-    return nullptr;
+    return LayoutFlowThread::locateFlowThreadContainingBlockOf(*this);
 }
 
 // FIXME: This could be used when changing the size of a layoutObject without children to skip some invalidations.
 // FIXME: This is incorrect for document element. Remove this when we enable slimming paint.
 static inline bool layoutObjectHasNoBoxEffectObsolete(const LayoutObject& object)
 {
     return !object.style()->hasVisualOverflowingEffect() && !object.style()->hasBorderDecoration() && !object.style()->hasBackground();
 }
 
 bool LayoutObject::skipInvalidationWhenLaidOutChildren() const
@@ skipping 2676 matching lines @@
         const blink::LayoutObject* root = object1;
         while (root->parent())
             root = root->parent();
         root->showLayoutTreeAndMark(object1, "*", object2, "-", 0);
     } else {
         fprintf(stderr, "Cannot showLayoutTree. Root is (nil)\n");
     }
 }
 
 #endif