Implement type variables in mixin applications.

pkg/front_end/lib/src/fasta/dill/dill_class_builder.dart

Index: pkg/front_end/lib/src/fasta/dill/dill_class_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/dill/dill_class_builder.dart b/pkg/front_end/lib/src/fasta/dill/dill_class_builder.dart
index 4c97dd2006e9aaa8b22ce1ef1f4a852a44e4b919..6511ca85838093e6c985c985ab21755ec216fc8b 100644
--- a/pkg/front_end/lib/src/fasta/dill/dill_class_builder.dart
+++ b/pkg/front_end/lib/src/fasta/dill/dill_class_builder.dart
@@ -11,9 +11,13 @@ import 'package:kernel/ast.dart' show
     Procedure,
     ProcedureKind;
 
+import '../errors.dart' show
+    internalError;
+
 import '../kernel/kernel_builder.dart' show
     Builder,
-    KernelClassBuilder;
+    KernelClassBuilder,
+    TypeBuilder;
 
 import '../modifier.dart' show
     abstractMask;
@@ -50,6 +54,12 @@ class DillClassBuilder extends KernelClassBuilder {
     }
   }
 
+  /// Returns true if this class is the result of applying a mixin to its
+  /// superclass.
+  bool get isMixinApplication => cls.isMixinApplication;
+
+  TypeBuilder get mixedInType => internalError("Not implemented.");
+
   Builder findConstructorOrFactory(String name) => constructors[name];
 }