Introduce OpenWorld.

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

Index: pkg/compiler/lib/src/js_backend/backend.dart
diff --git a/pkg/compiler/lib/src/js_backend/backend.dart b/pkg/compiler/lib/src/js_backend/backend.dart
index 64f6a8564aa64456778ad96777a28de801b5151c..6650db7073f640499f6ff8f9ff370efa784db55b 100644
--- a/pkg/compiler/lib/src/js_backend/backend.dart
+++ b/pkg/compiler/lib/src/js_backend/backend.dart
@@ -908,7 +908,7 @@ class JavaScriptBackend extends Backend {
     if (elements == null) return false;
     if (elements.isEmpty) return false;
     return elements.any((element) {
-      return selector.applies(element, compiler.closedWorld) &&
+      return selector.applies(element, this) &&
           (mask == null ||
               mask.canHit(element, selector, compiler.closedWorld));
     });
@@ -2871,7 +2871,7 @@ class JavaScriptImpactTransformer extends ImpactTransformer {
         case TypeUseKind.TYPE_LITERAL:
           backend.customElementsAnalysis.registerTypeLiteral(type);
           if (type.isTypedef) {
-            backend.compiler.openWorld.allTypedefs.add(type.element);
+            backend.compiler.openWorld.registerTypedef(type.element);
           }
           if (type.isTypeVariable && type is! MethodTypeVariableType) {
             // GENERIC_METHODS: The `is!` test above filters away method type