Support presentational iframes and make use of them in the uber frame.

content/browser/accessibility/browser_accessibility.h

Index: content/browser/accessibility/browser_accessibility.h
diff --git a/content/browser/accessibility/browser_accessibility.h b/content/browser/accessibility/browser_accessibility.h
index 6318e64b53d57043757c69a01388ca5c0e63c35f..6b6361df29d195c3914002d3398c029f2446faf0 100644
--- a/content/browser/accessibility/browser_accessibility.h
+++ b/content/browser/accessibility/browser_accessibility.h
@@ -244,6 +244,9 @@ class CONTENT_EXPORT BrowserAccessibility {
   // Returns true if this node is an editable text field of any kind.
   bool IsEditableText() const;
 
+  // True if this is a web area, and its grandparent is a presentational iframe.
+  bool IsWebAreaForPresentationalIframe() const;
+
   // Append the text from this node and its children.
   std::string GetTextRecursive() const;