[FastTextAutosizer] Check for containingBlock in deepestBlockContainingAllText

Source/core/rendering/FastTextAutosizer.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 903 matching lines @@
     }
 
     if (firstNode->isRenderBlock())
         return toRenderBlock(firstNode);
 
     // containingBlock() should never leave the cluster, since it only skips ancestors when finding
     // the container of position:absolute/fixed blocks, and those cannot exist between a cluster and
     // its text node's lowest common ancestor as isAutosizingCluster would have made them into their
     // own independent cluster.
     const RenderBlock* containingBlock = firstNode->containingBlock();
+    if (!containingBlock)
+        return root;
+
     ASSERT(containingBlock->isDescendantOf(root));
-
     return containingBlock;
 }
 
 const RenderObject* FastTextAutosizer::findTextLeaf(const RenderObject* parent, size_t& depth, TextLeafSearch firstOrLast)
 {
     // List items are treated as text due to the marker.
     // The actual renderer for the marker (RenderListMarker) may not be in the tree yet since it is added during layout.
     if (parent->isListItem())
         return parent;
 
@@ skipping 182 matching lines @@
 FastTextAutosizer::DeferUpdatePageInfo::~DeferUpdatePageInfo()
 {
     if (FastTextAutosizer* textAutosizer = m_mainFrame->document()->fastTextAutosizer()) {
         ASSERT(textAutosizer->m_updatePageInfoDeferred);
         textAutosizer->m_updatePageInfoDeferred = false;
         textAutosizer->updatePageInfoInAllFrames();
     }
 }
 
 } // namespace WebCore