More String + elimination in tests

tests/standalone/crypto/base64_test.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.
 
 #source("../../../runtime/bin/base64.dart");
 
 void main() {
   String line;
   String expected;
 
   line =
-      "Man is distinguished, not only by his reason, but by this singular " +
-      "passion from other animals, which is a lust of the mind, that by a " +
-      "perseverance of delight in the continued and indefatigable generation " +
+      "Man is distinguished, not only by his reason, but by this singular "
+      "passion from other animals, which is a lust of the mind, that by a "
+      "perseverance of delight in the continued and indefatigable generation "
       "of knowledge, exceeds the short vehemence of any carnal pleasure.";
   expected =
       "TWFuIGlzIGRpc3Rpbmd1aXNoZWQsIG5vdCBvbm"
       "x5IGJ5IGhpcyByZWFzb24sIGJ1dCBieSB0aGlz\r\n"
       "IHNpbmd1bGFyIHBhc3Npb24gZnJvbSBvdGhlci"
       "BhbmltYWxzLCB3aGljaCBpcyBhIGx1c3Qgb2Yg\r\n"
       "dGhlIG1pbmQsIHRoYXQgYnkgYSBwZXJzZXZlcm"
       "FuY2Ugb2YgZGVsaWdodCBpbiB0aGUgY29udGlu\r\n"
       "dWVkIGFuZCBpbmRlZmF0aWdhYmxlIGdlbmVyYX"
       "Rpb24gb2Yga25vd2xlZGdlLCBleGNlZWRzIHRo\r\n"
@@ skipping 35 matching lines @@
   for (int i = 0; i < 251; i++) {
     List<int> x = [i, i + 1, i + 2, i + 3, i + 4, i + 5];
     Expect.listEquals(x, _Base64._decode(_Base64._encode(x)));
   }
 
   for (int i = 0; i < 250; i++) {
     List<int> x = [i, i + 1, i + 2, i + 3, i + 4, i + 5, i + 6];
     Expect.listEquals(x, _Base64._decode(_Base64._encode(x)));
   }
 }