All strong mode cleaning of dart2js.

pkg/compiler/lib/src/constants/constructors.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.constants.constructors;
 
 import '../elements/entities.dart' show FieldEntity;
 import '../elements/types.dart';
 import '../universe/call_structure.dart' show CallStructure;
 import '../util/util.dart';
@@ skipping 21 matching lines @@
       EvaluationEnvironment environment,
       List<ConstantExpression> arguments,
       CallStructure callStructure);
 
   accept(ConstantConstructorVisitor visitor, arg);
 }
 
 abstract class ConstantConstructorVisitor<R, A> {
   const ConstantConstructorVisitor();
 
-  R visit(ConstantConstructor constantConstructor, A context) {
+  R visit(
+      covariant ConstantConstructor constantConstructor, covariant A context) {
     return constantConstructor.accept(this, context);
   }
 
-  R visitGenerative(GenerativeConstantConstructor constructor, A arg);
+  R visitGenerative(
+      covariant GenerativeConstantConstructor constructor, covariant A arg);
   R visitRedirectingGenerative(
-      RedirectingGenerativeConstantConstructor constructor, A arg);
+      covariant RedirectingGenerativeConstantConstructor constructor,
+      covariant A arg);
   R visitRedirectingFactory(
-      RedirectingFactoryConstantConstructor constructor, A arg);
+      covariant RedirectingFactoryConstantConstructor constructor,
+      covariant A arg);
 }
 
 /// A generative constant constructor.
 class GenerativeConstantConstructor implements ConstantConstructor {
   final InterfaceType type;
   final Map<dynamic /*int|String*/, ConstantExpression> defaultValues;
   final Map<FieldEntity, ConstantExpression> fieldMap;
   final ConstructedConstantExpression superConstructorInvocation;
 
   GenerativeConstantConstructor(this.type, this.defaultValues, this.fieldMap,
@@ skipping 186 matching lines @@
   }
 
   String toString() {
     StringBuffer sb = new StringBuffer();
     sb.write("{");
     sb.write("'constructor': ${targetConstructorInvocation.toDartText()}");
     sb.write("}");
     return sb.toString();
   }
 }