Fix warnings in dart2js.

dart/lib/compiler/implementation/apiimpl.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #library('leg_apiimpl');
 
 #import('dart:uri');
 
 #import('../compiler.dart', prefix: 'api');
 #import('leg.dart', prefix: 'leg');
@@ skipping 63 matching lines @@
     }
     elements.LibraryElement library =
         scanner.loadLibrary(uri, null, canonicalUri);
     return library;
   }
 
   void log(message) {
     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 = "";
     try {
       // TODO(ahe): We expect the future to be complete and call value
       // directly. In effect, we don't support truly asynchronous API.
       text = provider(translated).value;
     } catch (exception) {
       if (node !== null) {
         cancel("$exception", node: node);
@@ skipping 57 matching lines @@
       handler(translateUri(span.uri, null), span.begin, span.end,
               message, kind);
     }
   }
 
   bool get isMockCompilation {
     return mockableLibraryUsed
       && (options.indexOf('--allow-mock-compilation') !== -1);
   }
 }