Fix issue where iframe content wasn't included in the accessibility tree.

Source/core/rendering/RenderWidget.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2000 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2006, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 186 matching lines @@
 
             if (style()->visibility() != VISIBLE)
                 m_widget->hide();
             else {
                 m_widget->show();
                 repaint();
             }
         }
         moveWidgetToParentSoon(m_widget.get(), m_frameView);
     }
+
+    if (AXObjectCache* cache = document()->existingAXObjectCache())

[aboxhall, 2013/05/22 16:05:10]

Can you help me understand under what circumstances the cache would or would not
exist? Or is this just a defensive check?

[dmazzoni, 2013/05/22 16:28:13]

The cache shouldn't exist if accessibility is disabled in this
renderer, or if this document is not yet attached to the page.

We could check AXObjectCache::accessibilityEnabled() - however
if we did that we'd probably still want to call
existingAXObjectCache and check if it exists, because there
are some corner cases where accessibility is enabled but we
don't want an AXObjectCache for one particular document (like
if that document is not yet attached to the page).

So most of the time, code that needs to update the accessibility
tree can just do so if there's an AXObjectCache for the current
document and not otherwise. In just a few places we carefully
create the cache if it doesn't already exist.

+        cache->childrenChanged(this);
 }
 
 void RenderWidget::layout()
 {
     StackStats::LayoutCheckPoint layoutCheckPoint;
     ASSERT(needsLayout());
 
     setNeedsLayout(false);
 }
 
@@ skipping 160 matching lines @@
 CursorDirective RenderWidget::getCursor(const LayoutPoint& point, Cursor& cursor) const
 {
     if (widget() && widget()->isPluginView()) {
         // A plug-in is responsible for setting the cursor when the pointer is over it.
         return DoNotSetCursor;
     }
     return RenderReplaced::getCursor(point, cursor);
 }
 
 } // namespace WebCore