All strong mode cleaning of dart2js.

tests/compiler/dart2js/analyze_helper.dart

 // Copyright (c) 2016, 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 analyze_helper;
 
 import 'dart:async';
 import 'dart:io';
 import 'package:compiler/compiler.dart' as api;
 import 'package:compiler/src/apiimpl.dart';
@@ skipping 114 matching lines @@
             whiteListMap[file][messagePart]++;
             return true;
           }
         }
       }
     }
     return false;
   }
 
   @override
-  void report(Message message, Uri uri, int begin, int end, String text,
-      api.Diagnostic kind) {
+  void report(covariant Message message, Uri uri, int begin, int end,
+      String text, api.Diagnostic kind) {
     if (kind == api.Diagnostic.WARNING) {
       if (checkWhiteList(uri, message, text)) {
         // Suppress whitelisted warnings.
         lastWasWhitelisted = true;
         if (showWhitelisted || verbose) {
           super.report(message, uri, begin, end, text, kind);
         }
         return;
       }
       hasWarnings = true;
@@ skipping 137 matching lines @@
   if (checkResults != null) {
     result = checkResults(compiler, handler);
   } else {
     result = handler.checkResults();
   }
   if (!result) {
     print(MESSAGE);
     exit(1);
   }
 }