Support mixins when loading from .dill

pkg/compiler/lib/src/ssa/kernel_ast_adapter.dart

Index: pkg/compiler/lib/src/ssa/kernel_ast_adapter.dart
diff --git a/pkg/compiler/lib/src/ssa/kernel_ast_adapter.dart b/pkg/compiler/lib/src/ssa/kernel_ast_adapter.dart
index 02c6b36198d5a45ffdfb0bc50189b3d6778b5ff4..5ea20189a3df169c8faae1bb8200138f9c3c16bd 100644
--- a/pkg/compiler/lib/src/ssa/kernel_ast_adapter.dart
+++ b/pkg/compiler/lib/src/ssa/kernel_ast_adapter.dart
@@ -179,6 +179,12 @@ class KernelAstAdapter extends KernelToElementMapMixin {
   ConstructorElement getConstructor(ir.Member node) =>
       getElement(node).declaration;
 
+  @override
+  ConstructorEntity getSuperConstructor(
+      ir.Constructor constructor, ir.Member target) {
+    return getConstructor(target);
+  }
+
   MemberElement getMember(ir.Member node) => getElement(node).declaration;
 
   MethodElement getMethod(ir.Procedure node) => getElement(node).declaration;