Update charted to 0.4.8 and roll

packages/yaml/lib/src/loader.dart

Index: packages/yaml/lib/src/loader.dart
diff --git a/packages/yaml/lib/src/loader.dart b/packages/yaml/lib/src/loader.dart
index 07ae43051f8d8825341ab5e7c257a047a5f5f19e..a2d681b928cbd871bad17daaa1eb040f0c2fbc99 100644
--- a/packages/yaml/lib/src/loader.dart
+++ b/packages/yaml/lib/src/loader.dart
@@ -2,8 +2,6 @@
 // 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';
 
@@ -149,7 +147,7 @@ class Loader {
       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);
@@ -158,6 +156,10 @@ class Loader {
     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();
     }