Move Yaml into utils/pub.

utils/pub/yaml/yaml_map.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.
 
 /**
  * This class wraps behaves almost identically to the normal Dart Map
  * implementation, with the following differences:
  *
  * * It allows null, NaN, boolean, list, and map keys.
  * * It is itself Hashable.
@@ skipping 90 matching lines @@
       for (var e in obj) {
         hash ^= _hashCode(e, parents);
       }
       return hash;
     }
     return obj.hashCode();
   } finally {
     parents.removeLast();
   }
 }