Remove deprecated Strings class.

tests/utils/test_utils.dart

 // Copyright (c) 2011, 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.
 
 library test_utils;
 
 /**
  * Removes eight spaces of leading indentation from a multiline string.
  *
  * Note that this is very sensitive to how the literals are styled. They should
@@ skipping 12 matching lines @@
   if (lines.length <= 1) return text;
 
   for (var j = 0; j < lines.length; j++) {
     if (lines[j].length > 8) {
       lines[j] = lines[j].substring(8, lines[j].length);
     } else {
       lines[j] = '';
     }
   }
 
-  return Strings.join(lines, '\n');
+  return lines.join('\n');
 }
 
 /**
  * Indents each line of [text] so that, when passed to [cleanUpLiteral], it will
  * produce output identical to [text].
  *
  * This is useful for literals that need to include newlines but can't be
  * conveniently represented as multi-line strings.
  */
 // TODO(nweiz): Once cleanUpLiteral is fixed, get rid of this.
 String indentLiteral(String text) {
   var lines = text.split('\n');
   if (lines.length <= 1) return text;
 
   for (var i = 0; i < lines.length; i++) {
     lines[i] = "        ${lines[i]}";
   }
 
-  return Strings.join(lines, "\n");
+  return lines.join("\n");
 }