Introduce OpenWorld.

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

Index: pkg/compiler/lib/src/js_emitter/parameter_stub_generator.dart
diff --git a/pkg/compiler/lib/src/js_emitter/parameter_stub_generator.dart b/pkg/compiler/lib/src/js_emitter/parameter_stub_generator.dart
index aefe9162d63896b0687e265e9e3a455dcdcf91d6..d18c4bed666997f6f88cbbee220c7560a790c67b 100644
--- a/pkg/compiler/lib/src/js_emitter/parameter_stub_generator.dart
+++ b/pkg/compiler/lib/src/js_emitter/parameter_stub_generator.dart
@@ -248,7 +248,7 @@ class ParameterStubGenerator {
           new Selector.call(member.memberName, selector.callStructure);
       renamedCallSelectors.add(renamedSelector);
 
-      if (!renamedSelector.appliesUnnamed(member, compiler.closedWorld))
+      if (!renamedSelector.appliesUnnamed(member, backend))
         continue;
 
       if (untypedSelectors.add(renamedSelector)) {
@@ -265,7 +265,7 @@ class ParameterStubGenerator {
     // call-selectors (and they are in the renamedCallSelectors set.
     for (Selector selector in selectors.keys) {
       if (renamedCallSelectors.contains(selector)) continue;
-      if (!selector.appliesUnnamed(member, compiler.closedWorld)) continue;
+      if (!selector.appliesUnnamed(member, backend)) continue;
       if (!selectors[selector]
           .applies(member, selector, compiler.closedWorld)) {
         continue;