add IID for use with nsCOMPtr.

base/src/nsIAtom.h

@@ -35,6 +35,8 @@ class nsISizeOfHandler;
  */
 class nsIAtom : public nsISupports {
 public:
+  static const nsIID& IID() { static nsIID iid = NS_IATOM_IID; return iid; }
+
   /**
    * Translate the unicode string into the stringbuf.
    */

xpcom/ds/nsIAtom.h

@@ -35,6 +35,8 @@ class nsISizeOfHandler;
  */
 class nsIAtom : public nsISupports {
 public:
+  static const nsIID& IID() { static nsIID iid = NS_IATOM_IID; return iid; }
+
   /**
    * Translate the unicode string into the stringbuf.
    */