Update unittest to new package layout.

pkg/unittest/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.
-/**
- * The default implementation of IDescription. This should rarely need
- * substitution, although conceivably it is a place where other languages
- * could be supported.
- */
-
-class StringDescription implements Description {
-  var _out;
-
-  /** Initialize the description with initial contents [init]. */
-  StringDescription([String init = '']) {
-    _out = init;
-  }
-
-  /** Get the description as a string. */
-  String toString() => _out;
-
-  /** 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
-   * escaping any embedded control characters; otherwise use its
-   * toString() value and wrap it in angular "quotes".
-   */
-  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 {
-        add('<');
-        add(description);
-        add('>');
-      }
-    }
-    return this;
-  }
-
-  /**
-   * Append an [Iterable] [list] of objects to the description, using the
-   * specified [separator] and framing the list with [start]
-   * and [end].
-   */
-  Description addAll(String start, String separator, String end,
-                       Iterable list) {
-    var separate = false;
-    add(start);
-    for (var item in list) {
-      if (separate) {
-        add(separator);
-      }
-      addDescriptionOf(item);
-      separate = true;
-    }
-    add(end);
-    return this;
-  }
-
-  /** Escape the control characters in [string] so that they are visible. */
-  _addEscapedString(String string) {
-    add("'");
-    for (var i = 0; i < string.length; i++) {
-      add(_escape(string[i]));
-    }
-    add("'");
-  }
-
-  /** Return the escaped form of a character [ch]. */
-  _escape(ch) {
-    if (ch == "'")
-      return "\'";
-    else if (ch == '\n')
-      return '\\n';
-    else if (ch == '\r')
-      return '\\r';
-    else if (ch == '\t')
-      return '\\t';
-    else
-      return ch;
-  }
-}