Move towards using WorldImpact for codegen

pkg/compiler/lib/src/js_backend/backend_impact.dart

 // Copyright (c) 2015, 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.js_helpers.impact;
 
 import '../compiler.dart' show Compiler;
 import '../core_types.dart' show CommonElements;
 import '../dart_types.dart' show InterfaceType;
 import '../elements/elements.dart' show ClassElement, Element;
 import 'backend_helpers.dart';
 import 'constant_system_javascript.dart';
 import 'js_backend.dart';
 
 /// A set of JavaScript backend dependencies.
 class BackendImpact {
   final List<Element> staticUses;
   final List<InterfaceType> instantiatedTypes;
   final List<ClassElement> instantiatedClasses;
   final List<BackendImpact> otherImpacts;
 
-  BackendImpact(
+  const BackendImpact(
       {this.staticUses: const <Element>[],
       this.instantiatedTypes: const <InterfaceType>[],
       this.instantiatedClasses: const <ClassElement>[],
       this.otherImpacts: const <BackendImpact>[]});
 }
 
 /// The JavaScript backend dependencies for various features.
 class BackendImpacts {
   final Compiler compiler;
 
@@ skipping 563 matching lines @@
 
   BackendImpact _closure;
 
   BackendImpact get closure {
     if (_closure == null) {
       _closure = new BackendImpact(
           instantiatedClasses: [commonElements.functionClass]);
     }
     return _closure;
   }
+
+  BackendImpact _interceptorUse;
+
+  BackendImpact get interceptorUse {

[Harry Terkelsen, 2016/09/19 21:17:52]

consider doing:
_interceptorUse ??= ...
instead

+    if (_interceptorUse == null) {
+      _interceptorUse = new BackendImpact(staticUses: [
+        helpers.getNativeInterceptorMethod
+      ], instantiatedClasses: [
+        helpers.jsJavaScriptObjectClass,
+        helpers.jsPlainJavaScriptObjectClass,
+        helpers.jsJavaScriptFunctionClass
+      ]);
+    }
+    return _interceptorUse;
+  }
 }