dart2js: fix typos

pkg/compiler/lib/src/dump_info.dart

 // Copyright (c) 2013, 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 dump_info;
 
 import 'dart:convert'
     show HtmlEscape, JsonEncoder, StringConversionSink, ChunkedConversionSink;
 
 import 'elements/elements.dart';
@@ skipping 349 matching lines @@
    * function body
    */
   void elementUsesSelector(Element element, UniverseSelector selector) {
     if (compiler.dumpInfo) {
       selectorsFromElement
           .putIfAbsent(element, () => new Set<UniverseSelector>())
           .add(selector);
     }
   }
 
-  final Map<Element, List<Element>> _dependencies = {};
+  final Map<Element, Set<Element>> _dependencies = {};
   void registerDependency(Element source, Element target) {
     _dependencies.putIfAbsent(source, () => new Set()).add(target);
   }
 
   /**
    * Returns an iterable of [Selection]s that are used by
    * [element].  Each [Selection] contains an element that is
    * used and the selector that selected the element.
    */
   Iterable<Selection> getRetaining(Element element) {
@@ skipping 144 matching lines @@
 
     ChunkedConversionSink<Object> sink = encoder.startChunkedConversion(
         new StringConversionSink.fromStringSink(buffer));
     sink.add(result.toJson());
     compiler.reportInfo(NO_LOCATION_SPANNABLE, MessageKind.GENERIC, {
       'text': "View the dumped .info.json file at "
           "https://dart-lang.github.io/dump-info-visualizer"
     });
   }
 }