Fix build breakage: full #include needed.

caps/idl/nsIScriptSecurityManager.idl

@@ -17,8 +17,8 @@
  */
 
 #include "nsISupports.idl"
+#include "nsIPrincipal.idl"
 
-interface nsIPrincipal;
 interface nsIScriptContext;
 interface nsIURI;