Resynthesize interfaces from Kernel.

pkg/analyzer/lib/src/dart/element/element.dart

 // Copyright (c) 2014, 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 analyzer.src.dart.element.element;
 
 import 'dart:collection';
 import 'dart:math' show min;
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 728 matching lines @@
     for (PropertyAccessorElement accessor in accessors) {
       if (accessor.isStatic) {
         return true;
       }
     }
     return false;
   }
 
   @override
   List<InterfaceType> get interfaces {
-    if (_unlinkedClass != null && _interfaces == null) {
-      ResynthesizerContext context = enclosingUnit.resynthesizerContext;
-      _interfaces = _unlinkedClass.interfaces
-          .map((EntityRef t) => context.resolveTypeRef(this, t))
-          .where(_isClassInterfaceType)
-          .toList(growable: false);
+    if (_interfaces == null) {
+      if (_kernel != null) {
+        _interfaces = _kernel.implementedTypes
+            .map((k) => enclosingUnit._kernelContext.getInterfaceType(this, k))
+            .toList(growable: false);
+      }
+      if (_unlinkedClass != null) {
+        ResynthesizerContext context = enclosingUnit.resynthesizerContext;
+        _interfaces = _unlinkedClass.interfaces
+            .map((EntityRef t) => context.resolveTypeRef(this, t))
+            .where(_isClassInterfaceType)
+            .toList(growable: false);
+      }
     }
     return _interfaces ?? const <InterfaceType>[];
   }
 
   void set interfaces(List<InterfaceType> interfaces) {
     _assertNotResynthesized(_unlinkedClass);
     _interfaces = interfaces;
   }
 
   @override
@@ skipping 8336 matching lines @@
 
   @override
   DartObject computeConstantValue() => null;
 
   @override
   void visitChildren(ElementVisitor visitor) {
     super.visitChildren(visitor);
     _initializer?.accept(visitor);
   }
 }