A step towards handling `new Object()` in compile_from_dill_test

pkg/compiler/lib/src/universe/codegen_world_builder.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.
 
 part of world_builder;
 
 /// World builder specific to codegen.
 ///
 /// This adds additional access to liveness of selectors and elements.
 abstract class CodegenWorldBuilder implements WorldBuilder {
@@ skipping 598 matching lines @@
 
   @override
   void forEachParameter(
       FunctionEntity function, void f(DartType type, String name)) {
     throw new UnimplementedError('KernelCodegenWorldBuilder.forEachParameter');
   }
 
   @override
   void forEachInstanceField(
       ClassEntity cls, void f(ClassEntity declarer, FieldEntity field)) {
-    throw new UnimplementedError(
-        'KernelCodegenWorldBuilder.forEachInstanceField');
+    _elementEnvironment.forEachClassMember(cls,
+        (ClassEntity declarer, MemberEntity member) {
+      if (member.isField && member.isInstanceMember) f(declarer, member);
+    });
   }
 }