Implement is-checks for static functions.

sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart

Index: sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart
diff --git a/sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart b/sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart
index b70c32c2aaa78bac336c88971e1f1c5153986a08..3cb1dc84d5a28e970101aae03b2d04cbec8973ae 100644
--- a/sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart
+++ b/sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart
@@ -1251,6 +1251,7 @@ $lazyInitializerLogic
     buffer.add(functionBuffer);
     buffer.add('$N$n');
   }
+
   void emitStaticFunctionsWithNamer(CodeBuffer buffer,
                                     Map<Element, CodeBuffer> generatedCode,
                                     String functionNamer(Element element)) {
@@ -1293,6 +1294,15 @@ $lazyInitializerLogic
       // in case it is used in spawnFunction.
       String fieldName = namer.STATIC_CLOSURE_NAME_NAME;
       buffer.add('$fieldAccess.$fieldName$_=$_"$staticName"$N');
+      for (TypedefElement typedef in checkedTypedefs) {
+        FunctionType typedefType =
+            typedef.computeType(compiler).unalias(compiler);
+        if (compiler.types.isSubtype(element.computeType(compiler),
+                                     typedefType)) {
+          String operator = namer.operatorIs(typedef);
+          buffer.add('$fieldAccess.$operator$_=${_}true$N');
+        }
+      }
     }
   }