added empty impl of DoneAddingContent

b 17695, r=self

layout/html/forms/src/nsNativeSelectControlFrame.cpp

@@ -157,6 +157,7 @@ public:
   NS_IMETHOD RemoveOption(nsIPresContext* aPresContext, PRInt32 aIndex);
   NS_IMETHOD SetOptionSelected(PRInt32 aIndex, PRBool aValue);
   NS_IMETHOD GetOptionSelected(PRInt32 aIndex, PRBool* aValue);
+  NS_IMETHOD DoneAddingContent();
 
   //nsIStatefulFrame
   NS_IMETHOD GetStateType(nsIPresContext* aPresContext, nsIStatefulFrame::StateType* aStateType);
@@ -1160,6 +1161,12 @@ nsNativeSelectControlFrame::ControlChanged(nsIPresContext* aPresContext)
   }
 }
 
+NS_IMETHODIMP
+nsNativeSelectControlFrame::DoneAddingContent()
+{
+  return NS_OK;
+}
+
 // Get the selected state from the local cache
 void nsNativeSelectControlFrame::GetOptionSelectedCache(PRInt32 indx, PRBool* aValue)
 {