Fix tests in language suite: eliminate String +

tests/language/pseudo_kw_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.
 // Check that we can use pseudo keywords as names in function level code.
 
 
 class PseudoKWTest {
   static testMain() {
 
     // This is a list of built-in identifiers from the Dart spec.
@@ skipping 31 matching lines @@
     }
 
     get: while (import > 0) {
       break get;
     }
 
     return static + library * operator;
   }
 }
 
-typedef(x) => "typedef " + x;
+typedef(x) => "typedef $x";
 
 static(abstract) {
   return abstract == true;
 }
 
 class A {
   var typedef = 0;
   final operator = "smooth";
 
   set(x) { typedef = x; }
@@ skipping 41 matching lines @@
   Expect.equals(1, A.static());
   typedef("T");
   Expect.equals("typedef T", typedef("T"));
   static("true");
   Expect.equals(false, static("true"));
   Expect.equals(5, C.operator);
   Expect.equals(null, C.get);
   C.set = 0;
   Expect.equals(111, C.set);
 }