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

Source/core/rendering/RenderWidget.cpp

Index: Source/core/rendering/RenderWidget.cpp
diff --git a/Source/core/rendering/RenderWidget.cpp b/Source/core/rendering/RenderWidget.cpp
index 3f1a80056d52d87391f3282ad1118e2bcc0e0902..cf2d6e94fe1c05810539a99fd7d4e934fc2c2189 100644
--- a/Source/core/rendering/RenderWidget.cpp
+++ b/Source/core/rendering/RenderWidget.cpp
@@ -202,6 +202,9 @@ void RenderWidget::setWidget(PassRefPtr<Widget> widget)
         }
         moveWidgetToParentSoon(m_widget.get(), m_frameView);
     }
+
+    if (AXObjectCache* cache = document()->existingAXObjectCache())
+        cache->childrenChanged(this);
 }
 
 void RenderWidget::layout()