Pass ClosedWorld directly to codegen tasks

pkg/compiler/lib/src/ssa/graph_builder.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.
 
 import '../closure.dart';
 import '../common.dart';
 import '../common/codegen.dart' show CodegenRegistry;
 import '../compiler.dart';
 import '../dart_types.dart';
 import '../elements/elements.dart';
@@ skipping 24 matching lines @@
   Compiler compiler;
 
   /// The JavaScript backend we are targeting in this compilation.
   JavaScriptBackend get backend;
 
   /// The tree elements for the element being built into an SSA graph.
   TreeElements get elements;
 
   CodegenRegistry get registry;
 
-  ClosedWorld get closedWorld => compiler.closedWorld;
+  ClosedWorld get closedWorld;
 
   CommonMasks get commonMasks => closedWorld.commonMasks;
 
   GlobalTypeInferenceResults get globalInferenceResults =>
       compiler.globalInference.results;
 
   /// Used to track the locals while building the graph.
   LocalsHandler localsHandler;
 
   /// A stack of instructions.
@@ skipping 275 matching lines @@
     if (unaliased is TypedefType) throw 'unable to unalias $type';
     unaliased.accept(this, builder);
   }
 
   void visitDynamicType(DynamicType type, GraphBuilder builder) {
     JavaScriptBackend backend = builder.compiler.backend;
     ClassElement cls = backend.helpers.DynamicRuntimeType;
     builder.push(new HDynamicType(type, new TypeMask.exact(cls, closedWorld)));
   }
 }