Update charted to 0.4.8 and roll

packages/yaml/lib/src/loader.dart

 // Copyright (c) 2014, 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 yaml.loader;
-
 import 'package:charcode/ascii.dart';
 import 'package:source_span/source_span.dart';
 
 import 'equality.dart';
 import 'event.dart';
 import 'parser.dart';
 import 'yaml_document.dart';
 import 'yaml_exception.dart';
 import 'yaml_node.dart';
 
@@ skipping 125 matching lines @@
     return node;
   }
 
   /// Composes a mapping node.
   YamlNode _loadMapping(MappingStartEvent firstEvent) {
     if (firstEvent.tag != "!" && firstEvent.tag != null &&
         firstEvent.tag != "tag:yaml.org,2002:map") {
       throw new YamlException("Invalid tag for mapping.", firstEvent.span);
     }
 
-    var children = deepEqualsMap();
+    var children = deepEqualsMap/*<dynamic, YamlNode>*/();
     var node = new YamlMap.internal(
         children, firstEvent.span, firstEvent.style);
     _registerAnchor(firstEvent.anchor, node);
 
     var event = _parser.parse();
     while (event.type != EventType.MAPPING_END) {
       var key = _loadNode(event);
       var value = _loadNode(_parser.parse());
+      if (children.containsKey(key)) {
+        throw new YamlException("Duplicate mapping key.", key.span);
+      }
+
       children[key] = value;
       event = _parser.parse();
     }
 
     setSpan(node, firstEvent.span.expand(event.span));
     return node;
   }
 
   /// Parses a scalar according to its tag name.
   YamlScalar _parseByTag(ScalarEvent scalar) {
@@ skipping 179 matching lines @@
         case ".nan":
         case ".NaN":
         case ".NAN":
           return double.NAN;
       }
     }
 
     return null;
   }
 }