Strong mode cleaning of many dart2js tests.

tests/compiler/dart2js/type_checker_test.dart

 // Copyright (c) 2011, 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.
 
 import 'dart:async';
 
 import 'package:async_helper/async_helper.dart';
 import 'package:expect/expect.dart';
 
 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;
 import 'package:compiler/src/parser/element_listener.dart';
 import 'package:compiler/src/tree/tree.dart';
 import 'package:compiler/src/typechecker.dart';
 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;
 final MessageKind UNDEFINED_GETTER = MessageKind.UNDEFINED_GETTER;
 
 main() {
   List tests = [
     testSimpleTypes,
     testReturn,
     testFor,
@@ skipping 2754 matching lines @@
   TreeElements elements = compiler.resolveNodeStatement(node, element);
   TypeCheckerVisitor checker =
       new TypeCheckerVisitor(compiler, elements, compiler.types);
   DiagnosticCollector collector = compiler.diagnosticCollector;
   collector.clear();
   checker.analyze(node, mustHaveType: false);
   generateOutput(compiler, text);
   compareWarningKinds(text, warnings, collector.warnings);
   compareWarningKinds(text, hints, collector.hints);
 }