Handle null literal in compile_from_dill

pkg/compiler/lib/src/universe/element_world_builder.dart

Index: pkg/compiler/lib/src/universe/element_world_builder.dart
diff --git a/pkg/compiler/lib/src/universe/element_world_builder.dart b/pkg/compiler/lib/src/universe/element_world_builder.dart
index 0583059273d872074453c6c60a4a6fc979ea28a6..9eaf7244d370dfa7fddac882135bbc0b6bedf954 100644
--- a/pkg/compiler/lib/src/universe/element_world_builder.dart
+++ b/pkg/compiler/lib/src/universe/element_world_builder.dart
@@ -10,11 +10,10 @@ class ElementResolutionWorldBuilder extends ResolutionWorldBuilderBase {
   /// and classes.
   static bool useInstantiationMap = false;
 
-  final JavaScriptBackend _backend;
   final Resolution _resolution;
 
   ElementResolutionWorldBuilder(
-      this._backend,
+      JavaScriptBackend backend,
       this._resolution,
       NativeBasicData nativeBasicData,
       NativeDataBuilder nativeDataBuilder,
@@ -22,8 +21,9 @@ class ElementResolutionWorldBuilder extends ResolutionWorldBuilderBase {
       BackendUsageBuilder backendUsageBuilder,
       SelectorConstraintsStrategy selectorConstraintsStrategy)
       : super(
-            _backend.compiler.elementEnvironment,
+            backend.compiler.elementEnvironment,
             _resolution.commonElements,
+            backend.constantSystem,
             nativeBasicData,
             nativeDataBuilder,
             interceptorDataBuilder,
@@ -174,7 +174,7 @@ class ElementResolutionWorldBuilder extends ResolutionWorldBuilderBase {
     _closed = true;
     return _closedWorldCache = new ClosedWorldImpl(
         commonElements: _commonElements,
-        constantSystem: _backend.constantSystem,
+        constantSystem: _constantSystem,
         nativeData: _nativeDataBuilder.close(),
         interceptorData: _interceptorDataBuilder.close(),
         backendUsage: _backendUsageBuilder.close(),