Improve matcher descriptions that match against objects, and thus fix a bug

pkg/unittest/lib/src/description.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.
 
 part of matcher;
 
 /**
  * The default implementation of IDescription. This should rarely need
  * substitution, although conceivably it is a place where other languages
  * could be supported.
@@ skipping 29 matching lines @@
    */
   Description addDescriptionOf(value) {
     if (value is Matcher) {
       value.describe(this);
     } else if (value is String) {
       _addEscapedString(value);
     } else {
       String description = (value == null) ? "null" : value.toString();
       if (description.startsWith('<') && description.endsWith('>')) {
           add(description);
+      } else if (description.startsWith("Instance of")) {
+        add('<');
+        add(description);
+        add(':');
+        add(value.hashCode.toString());
+        add('>');
       } else {
         add('<');
         add(description);
         add('>');
       }
     }
     return this;
   }
 
   /**
@@ skipping 32 matching lines @@
     else if (ch == '\n')
       return '\\n';
     else if (ch == '\r')
       return '\\r';
     else if (ch == '\t')
       return '\\t';
     else
       return ch;
   }
 }