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

Source/core/dom/Document.cpp

Index: Source/core/dom/Document.cpp
diff --git a/Source/core/dom/Document.cpp b/Source/core/dom/Document.cpp
index e3ff783900ca656fd499106a88c7daf2f48be5c4..8ed7aa969e6d90e08185242a540ef6d32d090dd5 100644
--- a/Source/core/dom/Document.cpp
+++ b/Source/core/dom/Document.cpp
@@ -2359,7 +2359,7 @@ void Document::implicitClose()
 
     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