Don't dereference null pointer in FastTextAutosizer::getTentativeClusterRoots()

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 703 matching lines @@
 #endif
     return cluster;
 }
 
 FastTextAutosizer::Supercluster* FastTextAutosizer::getSupercluster(const RenderBlock* block)
 {
     Fingerprint fingerprint = m_fingerprintMapper.get(block);
     if (!fingerprint)
         return 0;
 
-    BlockSet* roots = &m_fingerprintMapper.getTentativeClusterRoots(fingerprint);
+    BlockSet* roots = m_fingerprintMapper.getTentativeClusterRoots(fingerprint);
     if (!roots || roots->size() < 2 || !roots->contains(block))
         return 0;
 
     SuperclusterMap::AddResult addResult = m_superclusters.add(fingerprint, PassOwnPtr<Supercluster>());
     if (!addResult.isNewEntry)
         return addResult.storedValue->value.get();
 
     Supercluster* supercluster = new Supercluster(roots);
     addResult.storedValue->value = adoptPtr(supercluster);
     return supercluster;
@@ skipping 332 matching lines @@
     assertMapsAreConsistent();
 #endif
     return true;
 }
 
 FastTextAutosizer::Fingerprint FastTextAutosizer::FingerprintMapper::get(const RenderObject* renderer)
 {
     return m_fingerprints.get(renderer);
 }
 
-FastTextAutosizer::BlockSet& FastTextAutosizer::FingerprintMapper::getTentativeClusterRoots(Fingerprint fingerprint)
+FastTextAutosizer::BlockSet* FastTextAutosizer::FingerprintMapper::getTentativeClusterRoots(Fingerprint fingerprint)
 {
-    return *m_blocksForFingerprint.get(fingerprint);
+    return m_blocksForFingerprint.get(fingerprint);
 }
 
 FastTextAutosizer::LayoutScope::LayoutScope(RenderBlock* block)
     : m_textAutosizer(block->document().fastTextAutosizer())
     , m_block(block)
 {
     if (!m_textAutosizer)
         return;
 
     if (m_textAutosizer->shouldHandleLayout())
@@ skipping 58 matching lines @@
         computedSize = multiplier * specifiedSize;
     } else {
         computedSize = multiplier * pleasantSize + gradientAfterPleasantSize * (specifiedSize - pleasantSize);
         if (computedSize < specifiedSize)
             computedSize = specifiedSize;
     }
     return computedSize;
 }
 
 } // namespace blink