Implement literal maps.

dart/frog/leg/lib/js_helper.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('js_helper');
 
 #import('coreimpl.dart');
 
 #source('date_helper.dart');
 #source('regexp_helper.dart');
@@ skipping 296 matching lines @@
 
 checkGrowable(list, reason) {
   if (JS('bool', @'!!($0.fixed$length)', list)) {
     throw new UnsupportedOperationException(reason);
   }
 }
 
 builtin$toString$0(var value) {
   if (JS('bool', @'typeof $0 == "object"', value)) {
     if (isJsArray(value)) {
-      return "Instance of 'List'";
+      return Collections.collectionToString(value);
+    } else {
+      return UNINTERCEPTED(value.toString());
     }
-    return UNINTERCEPTED(value.toString());
   }
   if (JS('bool', @'$0 === 0 && (1 / $0) < 0', value)) {
     return '-0.0';
   }
   if (value === null) return 'null';
   if (JS('bool', @'typeof $0 == "function"', value)) {
     return 'Closure';
   }
   return JS('string', @'String($0)', value);
 }
@@ skipping 959 matching lines @@
       }
     }
   } else if (JS('bool', @'$0 instanceof RangeError', ex)) {
     var message = JS('String', @'$0.message', ex);
     if (message.contains('call stack')) {
       return new StackOverflowException();
     }
   }
   return ex;
 }
+
+/**
+ * Called by generated code to build a map literal. [keyValuePairs] is
+ * a list of key, value, key, value, ..., etc.
+ */
+makeLiteralMap(List keyValuePairs) {
+  Iterator iterator = keyValuePairs.iterator();
+  Map result = new LinkedHashMap();
+  while (iterator.hasNext()) {
+    String key = iterator.next();
+    var value = iterator.next();
+    result[key] = value;
+  }
+  return result;
+}