Reapply "New implementation of {,Linked}Hash{Set,Map}."

sdk/lib/_internal/compiler/implementation/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 source_map_builder;
 
 import 'util/util.dart';
 import 'scanner/scannerlib.dart' show Token;
 import 'source_file.dart';
 
@@ skipping 116 matching lines @@
     }
 
     int sourceNameIndex = indexOf(sourceNameList, sourceName, sourceNameMap);
     encodeVLQ(output, sourceNameIndex - previousSourceNameIndex);
     previousSourceNameIndex = sourceNameIndex;
   }
 
   int indexOf(List<String> list, String value, Map<String, int> map) {
     return map.putIfAbsent(value, () {
       int index = list.length;
-      map[value] = index;
       list.add(value);
       return index;
     });
   }
 
   static void encodeVLQ(StringBuffer output, int value) {
     int signBit = 0;
     if (value < 0) {
       signBit = 1;
       value = -value;
@@ skipping 35 matching lines @@
 
   int getColumn() => sourceFile.getColumn(getLine(), token.charOffset);
 
   String getSourceName() {
     if (token.isIdentifier()) return token.slowToString();
     return null;
   }
 
   bool isValid() => token.charOffset < sourceFile.text.length;
 }