Fix checked mode.

frog/tests/leg/mock_compiler.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.
 
 #library('mock_compiler');
 
 #import("dart:uri");
 
 #import("../../../lib/compiler/implementation/elements/elements.dart");
 #import("../../../lib/compiler/implementation/leg.dart");
@@ skipping 16 matching lines @@
   ltB() {} leB() {} eqB() {} gtB() {} geB() {} eqNullB(a) {}
   iae(x) {throw x;} ioore(x) {throw x;}
   guard$array(x) { return x; }
   guard$num(x) { return x; }
   guard$string(x) { return x; }
   guard$stringOrArray(x) { return x; }
   index(a, index) {}
   indexSet(a, index, value) {}
   setRuntimeTypeInfo(a, b) {}
   getRuntimeTypeInfo(a) {}
-  stringConcat() {}
-  stringToString() {}''';
+  S() {}''';
 
 final String DEFAULT_INTERCEPTORSLIB = @'''
   add$1(receiver, value) {}
   get$length(receiver) {}
   filter(receiver, predicate) {}
   removeLast(receiver) {}
   iterator(receiver) {}
   next(receiver) {}
   hasNext(receiver) {}''';
 
@@ skipping 150 matching lines @@
   importLibrary(library, compiler.coreLibrary, compiler);
   return library;
 }
 
 class StringScript extends Script {
   final String code;
   StringScript(this.code) : super(null, null);
   String get text() => code;
   String get name() => "mock script";
 }