Oilpan: Prepare moving AXObject to heap

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 2109 matching lines @@
     m_activeHoverElement = nullptr;
     m_autofocusElement = nullptr;
 
     if (m_focusedElement.get()) {
         RefPtrWillBeRawPtr<Element> oldFocusedElement = m_focusedElement;
         m_focusedElement = nullptr;
         if (frameHost())
             frameHost()->chromeClient().focusedNodeChanged(oldFocusedElement.get(), nullptr);
     }
 
-    if (this == &axObjectCacheOwner())
+    if (this == &axObjectCacheOwner()) {
         clearAXObjectCache();
+    } else if (AXObjectCache* cache = existingAXObjectCache()) {
+        for (Element& element : ElementTraversal::descendantsOf(*this)) {
+            cache->remove(&element);

[dmazzoni, 2015/06/08 15:25:49]

What would happen if we called AXObjectCache::getOrCreate and passed it one of
these elements immediately after this call? Would it correctly return null
because these elements are not attached to a document?

What I'm worried about is that when we remove an element from the cache, that
triggers calling childrenChanged on the parent node - and in some cases that may
try to use element traversal to find the parent and construct a new AXObject
from it.

+        }
+    }
 
     m_layoutView = nullptr;
     ContainerNode::detach(context);
 
     styleEngine().didDetach();
 
     frameHost()->eventHandlerRegistry().documentDetached(*this);
 
     // If this Document is associated with a live DocumentLoader, the
     // DocumentLoader will take care of clearing the FetchContext. Deferring
@@ skipping 3534 matching lines @@
 #ifndef NDEBUG
 using namespace blink;
 void showLiveDocumentInstances()
 {
     WeakDocumentSet& set = 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().string().utf8().data());
 }
 #endif