Strong mode cleaning of many dart2js tests.

tests/compiler/dart2js/serialization/analysis_test_helper.dart

 // Copyright (c) 2015, 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.
 
 library dart2js.serialization_analysis_test;
 
 import 'dart:async';
 import 'package:async_helper/async_helper.dart';
 import 'package:expect/expect.dart';
 import 'package:compiler/src/commandline_options.dart';
-import 'package:compiler/src/compiler.dart';
 import 'package:compiler/src/filenames.dart';
 import '../memory_compiler.dart';
 import 'helper.dart';
 import 'test_data.dart';
 
 /// Number of tests that are not part of the automatic test grouping.
 int SKIP_COUNT = 0;
 
 /// Number of groups that the [TESTS] are split into.
 int SPLIT_COUNT = 5;
@@ skipping 37 matching lines @@
           "Unexpected error count.");
       Expect.equals(test.expectedWarningCount,
           diagnosticCollector.warnings.length, "Unexpected warning count.");
       Expect.equals(test.expectedHintCount, diagnosticCollector.hints.length,
           "Unexpected hint count.");
       Expect.equals(test.expectedInfoCount, diagnosticCollector.infos.length,
           "Unexpected info count.");
     }
   });
 }