Add optional message to assert in Dart2js - continued

tests/compiler/dart2js/mock_libraries.dart

 // Copyright (c) 2014, 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 for creating mock versions of platform and internal libraries.
 
 library mock_libraries;
 
 String buildLibrarySource(
     Map<String, String> elementMap,
@@ skipping 89 matching lines @@
 };
 
 const String DEFAULT_PATCH_CORE_SOURCE = r'''
 import 'dart:_js_helper';
 import 'dart:_interceptors';
 import 'dart:_isolate_helper';
 import 'dart:async';
 ''';
 
 const Map<String, String> DEFAULT_JS_HELPER_LIBRARY = const <String, String>{
+  'assertTest': 'assertTest(a) {}',
+  'assertThrow': 'assertThrow(a) {}',
   'assertHelper': 'assertHelper(a) {}',
   'assertIsSubtype': 'assertIsSubtype(subtype, supertype, message) {}',
   'assertSubtype': 'assertSubtype(object, isField, checks, asField) {}',
   'assertSubtypeOfRuntimeType': 'assertSubtypeOfRuntimeType(object, type) {}',
   'asyncHelper': 'asyncHelper(object, asyncBody, completer) {}',
   'boolConversionCheck': 'boolConversionCheck(x) {}',
   'boolTypeCast': 'boolTypeCast(value) {}',
   'boolTypeCheck': 'boolTypeCheck(value) {}',
   'checkSubtype': 'checkSubtype(object, isField, checks, asField) {}',
   'checkSubtypeOfRuntimeType': 'checkSubtypeOfRuntimeType(o, t) {}',
@@ skipping 241 matching lines @@
         _shrBothPositive(other) => 42;
         _shrReceiverPositive(other) => 42;
         _shrOtherPositive(other) => 42;
 
         abs() => (this is JSInt) ? 42 : 42.2;
         remainder(other) => (this is JSInt) ? 42 : 42.2;
         truncate() => 42;
       }''',
   'JSString': r'''
       class JSString extends Interceptor implements String, JSIndexable {
-        var split;
-        var length;
+        split(pattern) => [];
+        int get length => 42;
         operator[](index) {}
         toString() {}
         operator+(other) => this;
         codeUnitAt(index) => 42;
       }''',
   'JSUInt31': 'class JSUInt31 extends JSUInt32 {}',
   'JSUInt32': 'class JSUInt32 extends JSPositiveInt {}',
   'ObjectInterceptor': 'class ObjectInterceptor {}',
   'PlainJavaScriptObject': 'class PlainJavaScriptObject {}',
   'UnknownJavaScriptObject': 'class UnknownJavaScriptObject {}',
@@ skipping 54 matching lines @@
 
     const LookupMap(this._entries, [this._nestedMaps = const []])
         : _key = null, _value = null;
 
     const LookupMap.pair(this._key, this._value)
         : _entries = const [], _nestedMaps = const [];
     V operator[](K k) => null;
   }''',
   '_version': 'const _version = "0.0.1+1";',
 };