All strong mode cleaning of dart2js.

pkg/compiler/lib/src/io/source_information.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.source_information;
 
 import 'package:kernel/ast.dart' show Location;
 import '../common.dart';
 import '../elements/elements.dart'
     show
@@ skipping 29 matching lines @@
 
   /// Return a short textual representation of the source location.
   String get shortText;
 }
 
 /// Strategy for creating, processing and applying [SourceInformation].
 class SourceInformationStrategy {
   const SourceInformationStrategy();
 
   /// Create a [SourceInformationBuilder] for [member].
-  SourceInformationBuilder createBuilderForContext(MemberEntity member) {
+  SourceInformationBuilder createBuilderForContext(
+      covariant MemberEntity member) {
     return const SourceInformationBuilder();
   }
 
   /// Generate [SourceInformation] marker for non-preamble code.
   SourceInformation buildSourceMappedMarker() => null;
 
   /// Called when compilation has completed.
   void onComplete() {}
 }
 
 /// Interface for generating [SourceInformation].
 class SourceInformationBuilder {
   const SourceInformationBuilder();
 
   /// Create a [SourceInformationBuilder] for [member].
-  SourceInformationBuilder forContext(MemberEntity member) => this;
+  SourceInformationBuilder forContext(covariant MemberEntity member) => this;
 
   /// Generate [SourceInformation] the declaration of the [member].
-  SourceInformation buildDeclaration(MemberEntity member) => null;
+  SourceInformation buildDeclaration(covariant MemberEntity member) => null;
 
   /// Generate [SourceInformation] for the generic [node].
   @deprecated
   SourceInformation buildGeneric(Node node) => null;
 
   /// Generate [SourceInformation] for an instantiation of a class using [node]
   /// for the source position.
   SourceInformation buildCreate(Node node) => null;
 
   /// Generate [SourceInformation] for the return [node].
@@ skipping 239 matching lines @@
   @override
   int get line => null;
 
   @override
   int get offset => null;
 
   String get shortName => '<no-location>';
 
   String toString() => '<no-location>';
 }