Fix the weird names that can occur in exceptions and logs when there is no

lib/unittest/description.dart

Index: lib/unittest/description.dart
===================================================================
--- lib/unittest/description.dart	(revision 9562)
+++ lib/unittest/description.dart	(working copy)
@@ -10,26 +10,26 @@
 class StringDescription implements Description {
   var _out;
 
-  /**
-   * Initialize the description with initial contents [init].
-   */
+  /** Initialize the description with initial contents [init]. */
   StringDescription([String init = '']) {
     _out = init;
   }
 
-  /**
-   * Get the description as a string.
-   */
+  /** Get the description as a string. */
   String toString() => _out;
 
-  /**
-   * Append some plain [text] to the description.
-   */
+  /** Append some plain [text] to the description.  */
   Description add(String text) {
     _out = '${_out}${text}';
     return this;
   }
 
+  /** Change the value of the description. */
+  Description replace(String text) {
+    _out = text;
+    return this;
+  }
+
   /**
    * Appends a description of [value]. If it is an IMatcher use its
    * describe method; if it is a string use its literal value after