coverage: increase coverage of js_codegen

lib/src/codegen/js_codegen.dart

 // Copyright (c) 2015, 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 dev_compiler.src.codegen.js_codegen;
 
 import 'dart:collection' show HashSet;
 import 'dart:io' show Directory, File;
 
 import 'package:analyzer/analyzer.dart' hide ConstantEvaluator;
@@ skipping 1606 matching lines @@
     return list;
   }
 
   @override
   visitMapLiteral(MapLiteral node) {
     var entries = node.entries;
     var mapArguments = null;
     if (entries.isEmpty) return js.call('dart.map()');
 
     // Use JS object literal notation if possible, otherwise use an array.
-    if (entries.every((e) => e.key is SimpleStringLiteral)) {
+    // We could do this any time all keys are non-nullable String type.
+    // For now, support StringLiteral as the common non-nullable String case.
+    if (entries.every((e) => e.key is StringLiteral)) {
       var props = [];
       for (var e in entries) {
-        var key = (e.key as SimpleStringLiteral).value;
-        var value = _visit(e.value);
-        props.add(new JS.Property(js.escapedString(key), value));
+        props.add(new JS.Property(_visit(e.key), _visit(e.value)));
       }
       mapArguments = new JS.ObjectInitializer(props);
     } else {
       var values = [];
       for (var e in entries) {
         values.add(_visit(e.key));
         values.add(_visit(e.value));
       }
       mapArguments = new JS.ArrayInitializer(values);
     }
@@ skipping 396 matching lines @@
 
     // TODO(jmesserly): in many cases marking the end will be unncessary.
     printer.mark(_location(node.end));
   }
 
   String _getIdentifier(AstNode node) {
     if (node is SimpleIdentifier) return node.name;
     return null;
   }
 }