Improve DEFINE_STATIC_LOCAL()'s handling of Blink GCed objects.

third_party/WebKit/Source/core/dom/Document.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2008, 2009, 2011, 2012 Google Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) Research In Motion Limited 2010-2011. All rights reserved.
@@ skipping 345 matching lines @@
         *errorMessage = origin->isPotentiallyTrustworthyErrorMessage();
     return false;
 }
 
 uint64_t Document::s_globalTreeVersion = 0;
 
 static bool s_threadedParsingEnabledForTesting = true;
 
 Document::WeakDocumentSet& Document::liveDocumentSet()
 {
-    DEFINE_STATIC_LOCAL(Persistent<WeakDocumentSet>, set, (new WeakDocumentSet()));
-    return *set;
+    DEFINE_STATIC_LOCAL(WeakDocumentSet, set, (new WeakDocumentSet));
+    return set;
 }
 
 // This class doesn't work with non-Document ExecutionContext.
 class AutofocusTask final : public ExecutionContextTask {
 public:
     static PassOwnPtr<AutofocusTask> create()
     {
         return adoptPtr(new AutofocusTask());
     }
     ~AutofocusTask() override { }
@@ skipping 5652 matching lines @@
 #ifndef NDEBUG
 using namespace blink;
 void showLiveDocumentInstances()
 {
     Document::WeakDocumentSet& set = Document::liveDocumentSet();
     fprintf(stderr, "There are %u documents currently alive:\n", set.size());
     for (Document* document : set)
         fprintf(stderr, "- Document %p URL: %s\n", document, document->url().getString().utf8().data());
 }
 #endif