Strong mode cleaning of many dart2js tests.

tests/compiler/dart2js/type_checker_test.dart

Index: tests/compiler/dart2js/type_checker_test.dart
diff --git a/tests/compiler/dart2js/type_checker_test.dart b/tests/compiler/dart2js/type_checker_test.dart
index 0a3ec867739d6abf85f2ef7b6f866e1f96568a9d..f2b2952501f749a42d5341f6609840437e543674 100644
--- a/tests/compiler/dart2js/type_checker_test.dart
+++ b/tests/compiler/dart2js/type_checker_test.dart
@@ -11,7 +11,7 @@ import 'package:compiler/src/elements/resolution_types.dart';
 import 'package:compiler/src/diagnostics/messages.dart';
 import 'package:compiler/src/elements/elements.dart';
 import 'package:compiler/src/elements/modelx.dart'
-    show ClassElementX, CompilationUnitElementX, ElementX, FunctionElementX;
+    show ClassElementX, CompilationUnitElementX, ElementX;
 import 'package:compiler/src/io/source_file.dart';
 import 'package:compiler/src/resolution/tree_elements.dart'
     show TreeElements, TreeElementMapping;
@@ -22,7 +22,6 @@ import 'package:compiler/src/script.dart';
 import 'package:compiler/src/util/util.dart';
 
 import 'mock_compiler.dart';
-import 'options_helper.dart';
 import 'parser_helper.dart';
 
 final MessageKind NOT_ASSIGNABLE = MessageKind.NOT_ASSIGNABLE;