Issue #2532 - Implement form[method=dialog]

See bug 1557303

dom/html/HTMLInputElement.h

@@ -968,6 +968,8 @@ protected:
                                 const nsAttrValue* aOldValue,
                                 bool aNotify) override;
 
+  virtual void ResultForDialogSubmit(nsAString& aResult) override;
+  
   /**
    * Dispatch a select event. Returns true if the event was not cancelled.
    */