Implement methods in KernelClosedWorldMixin

pkg/compiler/lib/src/kernel/element_map_impl.dart

 // Copyright (c) 2017, 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.kernel.element_map;
 
 import 'package:kernel/ast.dart' as ir;
 
 import '../closure.dart' show BoxLocal;
 import '../common.dart';
@@ skipping 1577 matching lines @@
     if (element.isAbstract) {
       ClassEntity enclosingClass = element.enclosingClass;
       return hasConcreteMatch(
           elementEnvironment.getSuperClass(enclosingClass), selector);
     }
     return selector.appliesUntyped(element);
   }
 
   @override
   bool isNamedMixinApplication(ClassEntity cls) {
-    throw new UnimplementedError(
-        'KernelClosedWorldMixin.isNamedMixinApplication');
+    return elementMap._isMixinApplication(cls) &&
+        elementMap._isUnnamedMixinApplication(cls);
   }
 
   @override
   ClassEntity getAppliedMixin(ClassEntity cls) {
-    throw new UnimplementedError('KernelClosedWorldMixin.getAppliedMixin');
+    return elementMap._getAppliedMixin(cls);
   }
 
   @override
   Iterable<ClassEntity> getInterfaces(ClassEntity cls) {
-    throw new UnimplementedError('KernelClosedWorldMixin.getInterfaces');
+    return elementMap._getInterfaces(cls).map((t) => t.element);
   }
 
   @override
   ClassEntity getSuperClass(ClassEntity cls) {
     return elementMap._getSuperType(cls)?.element;
   }
 
   @override
   int getHierarchyDepth(ClassEntity cls) {
     return elementMap._getHierarchyDepth(cls);
@@ skipping 533 matching lines @@
   ///
   /// These names are not used in generated code, just as element name.
   String _getClosureVariableName(String name, int id) {
     return "_captured_${name}_$id";
   }
 
   String getDeferredUri(ir.LibraryDependency node) {
     throw new UnimplementedError('JsKernelToElementMap.getDeferredUri');
   }
 }