Fix warnings in dart2js.

dart/lib/compiler/implementation/apiimpl.dart

Index: dart/lib/compiler/implementation/apiimpl.dart
diff --git a/dart/lib/compiler/implementation/apiimpl.dart b/dart/lib/compiler/implementation/apiimpl.dart
index 4062ba6c8b7239dc5f3297208e66ba67d83569ac..477f3d26171be57c4ea9b12992a4ba3d334117b9 100644
--- a/dart/lib/compiler/implementation/apiimpl.dart
+++ b/dart/lib/compiler/implementation/apiimpl.dart
@@ -81,7 +81,7 @@ class Compiler extends leg.Compiler {
     handler(null, null, null, message, api.Diagnostic.VERBOSE_INFO);
   }
 
-  leg.Script readScript(Uri uri, [tree.Node node]) {
+  leg.Script readScript(Uri uri, [tree.LibraryTag node]) {
     if (uri.scheme == 'dart') uri = translateDartUri(uri, node);
     var translated = translateUri(uri, node);
     String text = "";