Create closed world for hello world using .dill file

pkg/compiler/lib/src/frontend_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.frontend_strategy;
 
 import 'common.dart';
 import 'common_elements.dart';
 import 'common/backend_api.dart';
 import 'common/tasks.dart';
@@ skipping 69 matching lines @@
   /// Creates the [MirrorsDataBuilder] for this strategy.
   MirrorsDataBuilder createMirrorsDataBuilder();
 
   /// Creates the [MirrorsResolutionAnalysis] for this strategy.
   // TODO(johnniwinther): Avoid passing [JavaScriptBackend].
   MirrorsResolutionAnalysis createMirrorsResolutionAnalysis(
       JavaScriptBackend backend);
 
   /// Creates the [RuntimeTypesNeedBuilder] for this strategy.
   RuntimeTypesNeedBuilder createRuntimeTypesNeedBuilder();
+
+  /// Creates a [SourceSpan] from [spannable] in context of [currentElement].
+  SourceSpan spanFromSpannable(Spannable spannable, Entity currentElement);
 }
 
 /// Class that performs the mechanics to investigate annotations in the code.
 abstract class AnnotationProcessor {
   void extractNativeAnnotations(
       LibraryEntity library, NativeBasicDataBuilder nativeBasicDataBuilder);
 
   void extractJsInteropAnnotations(
       LibraryEntity library, NativeBasicDataBuilder nativeBasicDataBuilder);
 
   void processJsInteropAnnotations(
       NativeBasicData nativeBasicData, NativeDataBuilder nativeDataBuilder);
 }