Bug 209475: Make nsIPermissionManager more flexible for extensions.

Changes nsIPermissionManager.idl to accept type strings rather than integers; this allows consumers to register unique types more easily, without fear of conflicting with an already-existing one.

Also fixes some bounds-checking fu (sr=bz on irc for those additional portions).

patch by mvl; r=dwitte, sr=bz.

netwerk/base/public/nsIPermission.idl

@@ -37,10 +37,13 @@ interface nsIPermission : nsISupports
     readonly attribute AUTF8String host;
 
     /**
-     * The type of permission (e.g., cookie, image, etc)
-     * (see nsIPermissionManager.idl for allowed values)
+     * a case-sensitive ASCII string, indicating the type of permission
+     * (e.g., "cookie", "image", etc).
+     * This string is specified by the consumer when adding a permission 
+     * via nsIPermissionManager.
+     * @see nsIPermissionManager
      */
-    readonly attribute PRUint32 type;
+    readonly attribute ACString type;
 
     /**
      * The permission (see nsIPermissionManager.idl for allowed values)