pkg/compiler: fix imports

pkg/compiler/lib/src/io/source_map_builder.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 dart2js.source_map_builder;
 
+import '../util/uri_extras.dart' show relativize;
 import '../util/util.dart';
-import '../util/uri_extras.dart' show relativize;
 import 'line_column_provider.dart';
 import 'source_information.dart' show SourceLocation;
 
 class SourceMapBuilder {
   /// The URI of the source map file.
   final Uri sourceMapUri;
 
   /// The URI of the target language file.
   final Uri targetFileUri;
 
@@ skipping 272 matching lines @@
   int register(T element) {
     return map.putIfAbsent(element, () => map.length);
   }
 
   /// Returns the index of [element].
   int operator [](T element) => map[element];
 
   /// Returns the indexed elements.
   Iterable<T> get elements => map.keys;
 }