UpdateWidget() can fire beforeload event synchronously blowing away RenderArena and its associated …

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 2341 matching lines @@
     if (!ownerElement() || (ownerElement()->renderer() && !ownerElement()->renderer()->needsLayout())) {
         updateStyleIfNeeded();
         
         // Always do a layout after loading if needed.
         if (view() && renderObject && (!renderObject->firstChild() || renderObject->needsLayout()))
             view()->layout();
     }
 
     m_processingLoadEvent = false;
 
-    if (f && renderObject && AXObjectCache::accessibilityEnabled()) {
+    if (f && renderObject && AXObjectCache::accessibilityEnabled() && axObjectCache()) {

[eseidel, 2013/04/23 20:37:51]

axObjectCache() isn't redundant with accessibilityEnabled? and doesn't cause one
to be lazyily created, correct?

[inferno, 2013/04/23 20:43:42]

It is not redundant with accessibilityEnabled. See
https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...

Let me check with Dominicc if it looks ok to him. 

[dmazzoni, 2013/04/23 20:54:07]

Nope, this creates an AXObjectCache. If you don't want to, use
existingAXObjectCache().

However, can you explain why you want to make this change? If accessibility is
enabled, we *want* to create an AXObjectCache at this point if there isn't one
already, otherwise the AXLoadComplete will never fire.

It this is causing a problem, we should fix it inside AXObjectCache.

[dmazzoni, 2013/04/23 21:08:41]

OK, so this is what you want.

As discussed offline, let's store it in a local -
that makes it more clear that you're creating it and just
checking if it's null, and it saves walking up to topDocument
3 - 4 times in a row.

         // The AX cache may have been cleared at this point, but we need to make sure it contains an
         // AX object to send the notification to. getOrCreate will make sure that an valid AX object
         // exists in the cache (we ignore the return value because we don't need it here). This is 
         // only safe to call when a layout is not in progress, so it can not be used in postNotification.    
         axObjectCache()->getOrCreate(renderObject);
         if (this == topDocument())
             axObjectCache()->postNotification(renderObject, AXObjectCache::AXLoadComplete, true);
         else {
             // AXLoadComplete can only be posted on the top document, so if it's a document
             // in an iframe that just finished loading, post AXLayoutComplete instead.
@@ skipping 3517 matching lines @@
         return;
 
     Vector<RefPtr<Element> > associatedFormControls;
     copyToVector(m_associatedFormControls, associatedFormControls);
 
     frame()->page()->chrome()->client()->didAssociateFormControls(associatedFormControls);
     m_associatedFormControls.clear();
 }
 
 } // namespace WebCore