Support for modular mixin resolution.

pkg/kernel/lib/target/targets.dart

Index: pkg/kernel/lib/target/targets.dart
diff --git a/pkg/kernel/lib/target/targets.dart b/pkg/kernel/lib/target/targets.dart
index f95cd92bb350397080e6a3b59f18245fbd9683d3..6ed22be2215f75383af0fe4adfaf7a07cc8cee03 100644
--- a/pkg/kernel/lib/target/targets.dart
+++ b/pkg/kernel/lib/target/targets.dart
@@ -4,10 +4,10 @@
 library kernel.target.targets;
 
 import '../ast.dart';
-
+import '../core_types.dart';
+import 'flutter.dart';
 import 'vm.dart';
 import 'vmcc.dart';
-import 'flutter.dart';
 
 final List<String> targetNames = targets.keys.toList();
 
@@ -49,6 +49,10 @@ abstract class Target {
   /// by the target.
   Map<String, String> get extraDeclaredVariables => const <String, String>{};
 
+  /// Classes from the SDK whose interface is required for the modular
+  /// transformations.
+  Map<String, List<String>> get requiredSdkClasses => CoreTypes.requiredClasses;
+
   bool get strongMode;
 
   /// If true, the SDK should be loaded in strong mode.