All strong mode cleaning of dart2js.

tests/compiler/dart2js/memory_compiler.dart

Index: tests/compiler/dart2js/memory_compiler.dart
diff --git a/tests/compiler/dart2js/memory_compiler.dart b/tests/compiler/dart2js/memory_compiler.dart
index df1772221a78a88ec3635ffca5b7268c9f7ab7a9..f19691290fbddaae9b1394195a9f17af83d48180 100644
--- a/tests/compiler/dart2js/memory_compiler.dart
+++ b/tests/compiler/dart2js/memory_compiler.dart
@@ -35,8 +35,8 @@ class MultiDiagnostics implements CompilerDiagnostics {
   const MultiDiagnostics([this.diagnosticsList = const []]);
 
   @override
-  void report(Message message, Uri uri, int begin, int end, String text,
-      Diagnostic kind) {
+  void report(covariant Message message, Uri uri, int begin, int end,
+      String text, Diagnostic kind) {
     for (CompilerDiagnostics diagnostics in diagnosticsList) {
       diagnostics.report(message, uri, begin, end, text, kind);
     }