Move towards using WorldImpact for codegen

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

Index: pkg/compiler/lib/src/js_backend/backend_impact.dart
diff --git a/pkg/compiler/lib/src/js_backend/backend_impact.dart b/pkg/compiler/lib/src/js_backend/backend_impact.dart
index 9a9a0d1a429d4c6531ad465377e25b654f23735d..8edd85d1be5ee50125fc536f97a8c377eb06665a 100644
--- a/pkg/compiler/lib/src/js_backend/backend_impact.dart
+++ b/pkg/compiler/lib/src/js_backend/backend_impact.dart
@@ -19,7 +19,7 @@ class BackendImpact {
   final List<ClassElement> instantiatedClasses;
   final List<BackendImpact> otherImpacts;
 
-  BackendImpact(
+  const BackendImpact(
       {this.staticUses: const <Element>[],
       this.instantiatedTypes: const <InterfaceType>[],
       this.instantiatedClasses: const <ClassElement>[],
@@ -603,4 +603,19 @@ class BackendImpacts {
     }
     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;
+  }
 }