One AXObjectCache per frame

public/web/WebViewClient.h

Index: public/web/WebViewClient.h
diff --git a/public/web/WebViewClient.h b/public/web/WebViewClient.h
index d690585b683518a147da0714e696b7bcf0b6b087..c2332510ddddb3b0146acfe7ebf5cd424b0bc186 100644
--- a/public/web/WebViewClient.h
+++ b/public/web/WebViewClient.h
@@ -188,6 +188,9 @@ public:
     // is the newly focused node. Either can be null.
     virtual void focusedNodeChanged(const WebNode& fromNode, const WebNode& toNode) { }
 
+    // Called when the focused frame changes.
+    virtual void focusedFrameChanged() { }
+
     // Indicates two things:
     //   1) This view may have a new layout now.
     //   2) Calling layout() is a no-op.