Strong mode cleaning of many dart2js tests.

tests/compiler/dart2js/import_mirrors_test.dart

 // Copyright (c) 2014, 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.
 
 // Test that the compiler emits a warning on import of 'dart:mirrors' unless
 // the flag --enable-experimental-mirrors is used.
 
 library dart2js.test.import_mirrors;
 
 import 'dart:async';
@@ skipping 298 matching lines @@
     expectedPaths = [expectedPaths];
   }
   var collector = new DiagnosticCollector();
   var options = [];
   if (verbose) {
     options.add('--verbose');
   }
   if (enableExperimentalMirrors) {
     options.add('--enable-experimental-mirrors');
   }
-  CompilationResult result = await runCompiler(
+  await runCompiler(
       entryPoint: Uri.parse('memory:/main.dart'),
       memorySourceFiles: sourceFiles,
       diagnosticHandler: collector,
       packageRoot: Uri.parse('memory:/pkg/'),
       options: options);
   Expect.equals(0, collector.errors.length, 'Errors: ${collector.errors}');
   if (enableExperimentalMirrors) {
     Expect.equals(
         0, collector.warnings.length, 'Warnings: ${collector.errors}');
   } else {
@@ skipping 36 matching lines @@
         DUAL_INDIRECT_IMPORT2,
         DUAL_INDIRECT_IMPORT3,
         DUAL_INDIRECT_PACKAGE_IMPORT1,
         DIRECT_EXPORT,
         INDIRECT_EXPORT1,
         INDIRECT_EXPORT2,
         INDIRECT_PACKAGE_EXPORT1,
         INDIRECT_PACKAGE_EXPORT2
       ], (map) => checkPaths(map)));
 }