Handle null literal in compile_from_dill

pkg/compiler/lib/src/universe/element_world_builder.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.
 
 part of world_builder;
 
 /// [ResolutionEnqueuerWorldBuilder] based on the [Element] model.
 class ElementResolutionWorldBuilder extends ResolutionWorldBuilderBase {
   /// Used for testing the new more precise computation of instantiated types
   /// and classes.
   static bool useInstantiationMap = false;
 
-  final JavaScriptBackend _backend;
   final Resolution _resolution;
 
   ElementResolutionWorldBuilder(
-      this._backend,
+      JavaScriptBackend backend,
       this._resolution,
       NativeBasicData nativeBasicData,
       NativeDataBuilder nativeDataBuilder,
       InterceptorDataBuilder interceptorDataBuilder,
       BackendUsageBuilder backendUsageBuilder,
       SelectorConstraintsStrategy selectorConstraintsStrategy)
       : super(
-            _backend.compiler.elementEnvironment,
+            backend.compiler.elementEnvironment,
             _resolution.commonElements,
+            backend.constantSystem,
             nativeBasicData,
             nativeDataBuilder,
             interceptorDataBuilder,
             backendUsageBuilder,
             selectorConstraintsStrategy);
 
   bool isImplemented(ClassElement cls) {
     return super.isImplemented(cls.declaration);
   }
 
@@ skipping 130 matching lines @@
 
   @override
   Iterable<InterfaceType> getSupertypes(ClassElement cls) => cls.allSupertypes;
 
   ClosedWorld closeWorld() {
     Map<ClassEntity, Set<ClassEntity>> typesImplementedBySubclasses =
         populateHierarchyNodes();
     _closed = true;
     return _closedWorldCache = new ClosedWorldImpl(
         commonElements: _commonElements,
-        constantSystem: _backend.constantSystem,
+        constantSystem: _constantSystem,
         nativeData: _nativeDataBuilder.close(),
         interceptorData: _interceptorDataBuilder.close(),
         backendUsage: _backendUsageBuilder.close(),
         resolutionWorldBuilder: this,
         functionSet: _allFunctions.close(),
         allTypedefs: _allTypedefs,
         mixinUses: _mixinUses,
         typesImplementedBySubclasses: typesImplementedBySubclasses,
         classHierarchyNodes: _classHierarchyNodes,
         classSets: _classSets);
   }
 
   @override
   void registerMixinUse(
       MixinApplicationElement mixinApplication, ClassElement mixin) {
     assert(mixin.isDeclaration);
     super.registerMixinUse(mixinApplication, mixin);
   }
 }