anchor.diff:    js_ast.Expression visitMapConstant(MapConstant node) {
       var entries = [
         for (var e in node.entries) ...[
  -        _visitConstant(e.key),
  -        _visitConstant(e.value),
  +        visitConstant(e.key),
  +        visitConstant(e.value),
         ],
       ];
       return _emitConstMap(node.keyType, node.valueType, entries);
  
positive.code:       _pendingClasses.addAll(l.classes);
      }
  
      // Add implicit dart:core dependency so it is first.
      emitLibraryName(_coreTypes.coreLibrary);
  
  
negative.code:   }
  
    js_ast.Fun _emitStaticFieldInitializer(Field field) {
      return js_ast.Fun([], js_ast.Block(_withLetScope(() {
        return [
          js_ast.Return(_visitInitializer(field.initializer, field.annotations))
        ];
      })));
    }
  
    List<js_ast.Statement> _withLetScope(List<js_ast.Statement> visitBody()) {
  