All strong mode cleaning of dart2js.

tests/compiler/dart2js/sourcemaps/mapping_test.dart

Index: tests/compiler/dart2js/sourcemaps/mapping_test.dart
diff --git a/tests/compiler/dart2js/sourcemaps/mapping_test.dart b/tests/compiler/dart2js/sourcemaps/mapping_test.dart
index 4d84ed073b4cf6e82661b573fbd026e19f07f659..a0cbf9199aa3e3cb9bed43635cbb28a01590cefc 100644
--- a/tests/compiler/dart2js/sourcemaps/mapping_test.dart
+++ b/tests/compiler/dart2js/sourcemaps/mapping_test.dart
@@ -3,21 +3,16 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:async';
-import 'dart:convert';
 import 'dart:io';
 
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/compiler_new.dart';
-import 'package:compiler/src/apiimpl.dart';
 import 'package:compiler/src/commandline_options.dart';
-import 'package:compiler/src/dart2js.dart' as entry;
 import 'package:expect/expect.dart';
 import 'package:source_maps/source_maps.dart';
-import 'package:source_maps/src/utils.dart';
 
 import '../annotated_code_helper.dart';
 import '../memory_compiler.dart';
-import '../source_map_validator_helper.dart';
 
 const List<String> TESTS = const <String>[
   '''