Create Namer and Emitter on codegen start.

pkg/compiler/lib/src/js_emitter/interceptor_stub_generator.dart

Index: pkg/compiler/lib/src/js_emitter/interceptor_stub_generator.dart
diff --git a/pkg/compiler/lib/src/js_emitter/interceptor_stub_generator.dart b/pkg/compiler/lib/src/js_emitter/interceptor_stub_generator.dart
index 265c946b25b08261d16b624c5b5e7ef720b12d69..9a7d2cc72fddcfb880536f18bb1fd7e0e3d54a84 100644
--- a/pkg/compiler/lib/src/js_emitter/interceptor_stub_generator.dart
+++ b/pkg/compiler/lib/src/js_emitter/interceptor_stub_generator.dart
@@ -8,8 +8,10 @@ class InterceptorStubGenerator {
   final Compiler compiler;
   final Namer namer;
   final JavaScriptBackend backend;
+  final ClosedWorld closedWorld;
 
-  InterceptorStubGenerator(this.compiler, this.namer, this.backend);
+  InterceptorStubGenerator(
+      this.compiler, this.namer, this.backend, this.closedWorld);
 
   Emitter get emitter => backend.emitter.emitter;
 
@@ -248,8 +250,8 @@ class InterceptorStubGenerator {
       bool containsJsIndexable =
           helpers.jsIndexingBehaviorInterface.isResolved &&
               classes.any((cls) {
-                return compiler.closedWorld
-                    .isSubtypeOf(cls, helpers.jsIndexingBehaviorInterface);
+                return closedWorld.isSubtypeOf(
+                    cls, helpers.jsIndexingBehaviorInterface);
               });
       // The index set operator requires a check on its set value in
       // checked mode, so we don't optimize the interceptor if the