More String + elimination in tests

tests/corelib/string_buffer_test.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.
 
 // TODO(srdjan): Move StringBuffer to visible names.
 
 class StringBufferTest {
   static testConstructor() {
     StringBuffer bf = new StringBuffer("");
     Expect.equals(true, bf.isEmpty());
@@ skipping 35 matching lines @@
     bf.add("s");
     bf.add("t");
     bf.add("u");
     bf.add("v");
     bf.add("w");
     bf.add("x");
     bf.add("y");
     bf.add("z");
     bf.add("\n");
     bf.add("thequickbrownfoxjumpsoverthelazydog");
-    Expect.equals("abcdefghijklmnopqrstuvwxyz\n" +
+    Expect.equals("abcdefghijklmnopqrstuvwxyz\n"
                   "thequickbrownfoxjumpsoverthelazydog",
                   bf.toString());
 
     bf = new StringBuffer("");
     for (int i = 0; i < 100000; i++) {
       bf.add('');
       bf.add("");
     }
     Expect.equals("", bf.toString());
 
@@ skipping 81 matching lines @@
     testAdd();
     testAddAll();
     testClear();
     testChaining();
   }
 }
 
 main() {
   StringBufferTest.testMain();
 }