kernel->ssa: implement assert statements

tests/compiler/dart2js/kernel/helper.dart

 // Copyright (c) 2016, 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.
 
 import 'dart:async';
 
 import 'package:compiler/src/compiler.dart' show Compiler;
 import 'package:compiler/src/elements/elements.dart' show Element;
 import 'package:compiler/src/js_backend/backend.dart' as js
     show JavaScriptBackend;
 import 'package:compiler/src/commandline_options.dart' show Flags;
 import 'package:test/test.dart';
 
 import '../memory_compiler.dart';
 
 Future<String> compile(String code,
     {String entry: 'main',
     bool useKernel: true,
-    bool disableTypeInference: true}) async {
+    bool disableTypeInference: true,
+    List<String> extraOptions: const <String>[]}) async {
   List<String> options = <String>[
     Flags.disableInlining,
   ];
   if (disableTypeInference) options.add(Flags.disableTypeInference);
   if (useKernel) options.add(Flags.useKernel);
+  options.addAll(extraOptions);
 
   if (entry != 'main' && !code.contains('main')) {
     code = "$code\n\nmain() => $entry;";
   }
   CompilationResult result = await runCompiler(
       memorySourceFiles: {'main.dart': code}, options: options);
   expect(result.isSuccess, isTrue);
   Compiler compiler = result.compiler;
   Element element = compiler.mainApp.find(entry);
   js.JavaScriptBackend backend = compiler.backend;
   return backend.getGeneratedCode(element);
 }
 
 Future check(String code,
-    {String entry: 'main', bool disableTypeInference: true}) async {
+    {String entry: 'main',
+    bool disableTypeInference: true,
+    List<String> extraOptions: const <String>[]}) async {
   var original = await compile(code,
       entry: entry,
       useKernel: false,
-      disableTypeInference: disableTypeInference);
+      disableTypeInference: disableTypeInference,
+      extraOptions: extraOptions);
   var kernel = await compile(code,
       entry: entry,
       useKernel: true,
-      disableTypeInference: disableTypeInference);
+      disableTypeInference: disableTypeInference,
+      extraOptions: extraOptions);
   expect(kernel, original);
 }