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 184 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())
+        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