Refactor LoopHandler to avoid calling KernelAstAdapter.getNode

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 259 matching lines @@
   JumpTarget getJumpTarget(ir.TreeNode node, {bool isContinueTarget: false}) {
     throw new UnimplementedError('KernelToLocalsMapImpl.getJumpTarget');
   }
 
   @override
   Local getLocal(ir.VariableDeclaration node) {
     return _map.putIfAbsent(node, () {
       return new KLocal(node.name, currentMember);
     });
   }
+
+  @override
+  ClosureScope getClosureScopeForLoop(
+      ClosureClassMap closureData, ir.TreeNode node) {
+    // TODO(johnniwinther): Support closure scopes for loops.
+    return null;
+  }
 }
 
 class KLocal implements Local {
   final String name;
   final MemberEntity memberContext;
 
   KLocal(this.name, this.memberContext);
 
   @override
   Entity get executableContext => memberContext;
@@ skipping 72 matching lines @@
   Iterable<ClassEntity> sortClasses(Iterable<ClassEntity> classes) {
     return classes.toList()
       ..sort((ClassEntity a, ClassEntity b) {
         int r = _compareLibraries(a.library, b.library);
         if (r != 0) return r;
         return _compareNodes(
             a, elementMap.getClassNode(a), b, elementMap.getClassNode(b));
       });
   }
 }