Use memory compiler in compiler_helper.dart.

tests/compiler/dart2js/semantic_visitor_test.dart

 // Copyright (c) 2015, 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 dart2js.semantics_visitor_test;
 
 import 'dart:async';
 import 'dart:mirrors';
 import 'package:async_helper/async_helper.dart';
 import 'package:expect/expect.dart';
+import 'package:compiler/src/commandline_options.dart';
 import 'package:compiler/src/constants/expressions.dart';
 import 'package:compiler/src/dart_types.dart';
 import 'package:compiler/src/diagnostics/spannable.dart';
 import 'package:compiler/src/diagnostics/messages.dart' show MessageKind;
 import 'package:compiler/src/compiler.dart';
 import 'package:compiler/src/elements/elements.dart';
 import 'package:compiler/src/resolution/operators.dart';
 import 'package:compiler/src/resolution/semantic_visitor.dart';
 import 'package:compiler/src/resolution/tree_elements.dart';
 import 'package:compiler/src/tree/tree.dart';
@@ skipping 264 matching lines @@
       mainSource.writeln("import '$filename';");
       testMap[filename] = test;
       index++;
     });
   });
   mainSource.writeln("main() {}");
   sourceFiles['main.dart'] = mainSource.toString();
 
   CompilationResult result = await runCompiler(
       memorySourceFiles: sourceFiles,
-      options: ['--analyze-all',
-                '--analyze-only',
-                '--enable-null-aware-operators']);
+      options: [Flags.analyzeAll, Flags.analyzeOnly]);
   Compiler compiler = result.compiler;
   testMap.forEach((String filename, Test test) {
     LibraryElement library = compiler.libraryLoader.lookupLibrary(
         Uri.parse('memory:$filename'));
     Element element;
     String cls = test.cls;
     String method = test.method;
     if (cls == null) {
       element = library.find(method);
     } else {
@@ skipping 445 matching lines @@
   ERROR_INVALID_INDEX_SET,
   ERROR_INVALID_COMPOUND_INDEX_SET,
   ERROR_INVALID_INDEX_PREFIX,
   ERROR_INVALID_INDEX_POSTFIX,
 
   VISIT_CONSTANT_GET,
   VISIT_CONSTANT_INVOKE,
 
   PREVISIT_DEFERRED_ACCESS,
 }