Merge kernel closure conversion into the Dart SDK

pkg/kernel/lib/transformations/closure/clone_without_body.dart

+// Copyright (c) 2016, 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 kernel.transformations.closure.converter;
+
+import '../../ast.dart' show
+    DartType,
+    FunctionNode,
+    TreeNode,
+    TypeParameter;
+
+import '../../clone.dart' show
+    CloneVisitor;
+
+class CloneWithoutBody extends CloneVisitor {
+  CloneWithoutBody({Map<TypeParameter, DartType> typeSubstitution})
+      : super(typeSubstitution: typeSubstitution);
+
+  @override
+  TreeNode cloneFunctionNodeBody(FunctionNode node) => null;
+}