34896, change to move constants to this file. r=hyatt

dom/public/idl/range/SelectionListener.idl

@@ -1,6 +1,10 @@
  interface SelectionListener {
 /* IID: { 0xa6cf90e2, 0x15b3, 0x11d2,             \
         { 0x93, 0x2e, 0x00, 0x80, 0x5f, 0x8a, 0xdd, 0x32} }		*/
+  const short NO_REASON=0;
+  const short DRAG_REASON=1;
+  const short MOUSEDOWN_REASON=2;/*bitflags*/
+  const short MOUSEUP_REASON=4;/*bitflags*/
 
 	void			notifySelectionChanged(in Document doc, in Selection sel, in short reason);
 };