All strong mode cleaning of dart2js.

pkg/compiler/lib/src/io/source_information.dart

Index: pkg/compiler/lib/src/io/source_information.dart
diff --git a/pkg/compiler/lib/src/io/source_information.dart b/pkg/compiler/lib/src/io/source_information.dart
index c2bb4ae3ec9d21ad78fd806b03f0d32e30888a04..371b038287a208a221c5b84fbf116e81266a0f22 100644
--- a/pkg/compiler/lib/src/io/source_information.dart
+++ b/pkg/compiler/lib/src/io/source_information.dart
@@ -47,7 +47,8 @@ class SourceInformationStrategy {
   const SourceInformationStrategy();
 
   /// Create a [SourceInformationBuilder] for [member].
-  SourceInformationBuilder createBuilderForContext(MemberEntity member) {
+  SourceInformationBuilder createBuilderForContext(
+      covariant MemberEntity member) {
     return const SourceInformationBuilder();
   }
 
@@ -63,10 +64,10 @@ 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