Create closed world for hello world using .dill file

pkg/compiler/lib/src/kernel/kernel_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.frontend_strategy;
 
 import '../closure.dart';
 import '../backend_strategy.dart';
 import '../common.dart';
 import '../common_elements.dart';
@@ skipping 113 matching lines @@
         selectorConstraintsStrategy);
   }
 
   WorkItemBuilder createResolutionWorkItemBuilder(
       NativeBasicData nativeBasicData,
       NativeDataBuilder nativeDataBuilder,
       ImpactTransformer impactTransformer) {
     return new KernelWorkItemBuilder(
         elementMap, nativeBasicData, nativeDataBuilder, impactTransformer);
   }
+
+  @override
+  SourceSpan spanFromSpannable(Spannable spannable, Entity currentElement) {
+    // TODO(johnniwinther): Compute source spans from kernel elements.
+    return new SourceSpan(null, null, null);
+  }
 }
 
 class KernelWorkItemBuilder implements WorkItemBuilder {
   final KernelToElementMapImpl _elementMap;
   final ImpactTransformer _impactTransformer;
   final NativeMemberResolver _nativeMemberResolver;
 
   KernelWorkItemBuilder(this._elementMap, NativeBasicData nativeBasicData,
       NativeDataBuilder nativeDataBuilder, this._impactTransformer)
       : _nativeMemberResolver = new KernelNativeMemberResolver(
@@ skipping 99 matching lines @@
   Sorter get sorter =>
       throw new UnimplementedError('KernelBackendStrategy.sorter');
 
   @override
   void convertClosures(ClosedWorldRefiner closedWorldRefiner) {
     // TODO(johnniwinther,efortuna): Compute closure classes for kernel based
     // elements.
     throw new UnimplementedError('KernelBackendStrategy.createClosureClasses');
   }
 }