Create new interface instead of ClosureClassMap for variable usage information that is not Element-…

pkg/compiler/lib/src/kernel/kernel_backend_strategy.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.backend_strategy;
 
 import 'package:kernel/ast.dart' as ir;
 
 import '../backend_strategy.dart';
 import '../closure.dart';
@@ skipping 198 matching lines @@
   @override
   TypeMask getReturnTypeOf(FunctionEntity function) {
     return _closedWorld.commonMasks.dynamicType;
   }
 }
 
 /// TODO(johnniwinther,efortuna): Implement this.
 class KernelClosureClassMaps implements ClosureClassMaps {
   const KernelClosureClassMaps();
 
+  // TODO(efortuna);
+  ClassEntity getClosureClassEntity(Local member);

[Johnni Winther, 2017/05/31 12:39:51]

Add a `=> null;` body to avoid warnings.

+
   @override
   ClosureClassMap getLocalFunctionMap(Local localFunction) {
     return new ClosureClassMap(null, null, null, null);
   }
 
   @override
   ClosureClassMap getMemberMap(MemberEntity member) {
     return new ClosureClassMap(null, null, null, null);
   }
 }