Add interfaces for a new compiler API.

tests/compiler/dart2js/mock_compiler.dart

Index: tests/compiler/dart2js/mock_compiler.dart
diff --git a/tests/compiler/dart2js/mock_compiler.dart b/tests/compiler/dart2js/mock_compiler.dart
index 3d879dfc9cc15a0b6799f869856fbe05d5150784..3284514de537b874d176ae13e21743ab7d2dc9cb 100644
--- a/tests/compiler/dart2js/mock_compiler.dart
+++ b/tests/compiler/dart2js/mock_compiler.dart
@@ -16,6 +16,7 @@ import 'package:compiler/src/js_backend/js_backend.dart'
 import 'package:compiler/src/resolution/resolution.dart';
 import 'package:compiler/src/io/source_file.dart';
 import 'package:compiler/src/tree/tree.dart';
+import 'package:compiler/src/old_to_new_api.dart';
 import 'package:compiler/src/util/util.dart';
 import 'parser_helper.dart';
 
@@ -93,7 +94,7 @@ class MockCompiler extends Compiler {
               preserveComments: preserveComments,
               trustTypeAnnotations: trustTypeAnnotations,
               showPackageWarnings: true,
-              outputProvider: outputProvider) {
+              outputProvider: new LegacyCompilerOutput(outputProvider)) {
     this.disableInlining = disableInlining;
 
     deferredLoadTask = new MockDeferredLoadTask(this);