Don't use "var" to introduce the deferred_initializer.

pkg/compiler/lib/src/js_emitter/startup_emitter/model_emitter.dart

Index: pkg/compiler/lib/src/js_emitter/startup_emitter/model_emitter.dart
diff --git a/pkg/compiler/lib/src/js_emitter/startup_emitter/model_emitter.dart b/pkg/compiler/lib/src/js_emitter/startup_emitter/model_emitter.dart
index 65d0519b357cf876b49338421e5249dfa45441a7..11826c37fa72fe91ce3ee5ab900866df65b16d59 100644
--- a/pkg/compiler/lib/src/js_emitter/startup_emitter/model_emitter.dart
+++ b/pkg/compiler/lib/src/js_emitter/startup_emitter/model_emitter.dart
@@ -252,10 +252,9 @@ class ModelEmitter {
   }
 
   js.Statement buildDeferredInitializerGlobal() {
-    String global = deferredInitializersGlobal;
-    return js.js.statement(
-        "if (typeof($global) === 'undefined') var # = Object.create(null);",
-        new js.VariableDeclaration(global, allowRename: false));
+    return js.js.statement('self.#deferredInitializers = '
+        'self.#deferredInitializers || Object.create(null);',
+        {'deferredInitializers': deferredInitializersGlobal});
   }
 
   // Writes the given [fragment]'s [code] into a file.