Require two type arguments for map literals (issue 4522).

lib/compiler/implementation/dart_backend/renamer.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.
 
 /**
  * Renames only top-level elements that would let to ambiguity if not renamed.
  * TODO(smok): Make sure that top-level fields are correctly renamed.
  */
 void renamePlaceholders(
     Compiler compiler,
     PlaceholderCollector placeholderCollector,
     Map<Node, String> renames,
     Map<LibraryElement, String> imports) {
   final Map<LibraryElement, Map<String, String>> renamed
       = new Map<LibraryElement, Map<String, String>>();
   final Set<String> usedTopLevelIdentifiers = new Set<String>();
   int privateNameCounter = 0;
 
   String getName(LibraryElement library, String originalName, renamer) =>
-      renamed.putIfAbsent(library, () => <String>{})
+      renamed.putIfAbsent(library, () => <String, String>{})
           .putIfAbsent(originalName, renamer);
 
   String renamePrivateIdentifier(LibraryElement library, String id) =>
       getName(library, id, () => '_${privateNameCounter++}${id}');
 
   Generator topLevelGenerator =
       true ? conservativeGenerator : new MinifyingGenerator('ABCD').generate;
   String generateUniqueName(name) {
     String newName = topLevelGenerator(
         name, usedTopLevelIdentifiers.contains);
@@ skipping 90 matching lines @@
     int length = alphabet.length;
     StringBuffer resultBuilder = new StringBuffer();
     while (index >= length) {
       resultBuilder.add(alphabet[index % length]);
       index ~/= length;
     }
     resultBuilder.add(alphabet[index]);
     return resultBuilder.toString();
   }
 }