Use new library/import syntax in dart2js.

sdk/lib/_internal/compiler/implementation/util/uri_extras.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('uri_extras');
+library uri_extras;
 
-#import('dart:math');
-#import('dart:uri');
+import 'dart:math';
+import 'dart:uri';
 
 String relativize(Uri base, Uri uri, bool isWindows) {
   if (!base.path.startsWith('/')) {
     // Also throw an exception if [base] or base.path is null.
     throw new ArgumentError('Expected absolute path: ${base.path}');
   }
   if (!uri.path.startsWith('/')) {
     // Also throw an exception if [uri] or uri.path is null.
     throw new ArgumentError('Expected absolute path: ${uri.path}');
   }
@@ skipping 37 matching lines @@
       sb.add('../');
     }
     for (int i = common; i < uriParts.length - 1; i++) {
       sb.add('${uriParts[i]}/');
     }
     sb.add('${uriParts.last}');
     return sb.toString();
   }
   return uri.toString();
 }