Fix exit_code_test after refactoring.

tests/compiler/dart2js/exit_code_test.dart

Index: tests/compiler/dart2js/exit_code_test.dart
diff --git a/tests/compiler/dart2js/exit_code_test.dart b/tests/compiler/dart2js/exit_code_test.dart
index ec9c16088c8d0e85de7cee55378c04e1cbb95b7b..11a04b1ae0176e6add099834948b45df478281bc 100644
--- a/tests/compiler/dart2js/exit_code_test.dart
+++ b/tests/compiler/dart2js/exit_code_test.dart
@@ -58,12 +58,18 @@ class TestCompiler extends apiimpl.CompilerImpl {
                 environment: environment,
                 packageConfig: packageConfig,
                 packagesDiscoveryProvider: findPackages)) {
-    scanner = new TestScanner(this);
-    resolver = new TestResolver(this, backend.constantCompilerTask);
     reporter = new TestDiagnosticReporter(this, super.reporter);
     test('Compiler');
   }
 
+  @override
+  ScannerTask createScannerTask() => new TestScanner(this);
+
+  @override
+  ResolverTask createResolverTask() {
+    return new TestResolver(this, backend.constantCompilerTask);
+  }
+
   Future<bool> run(Uri uri) {
     test('Compiler.run');
     return super.run(uri);