Check in codegen test expectations.

test/codegen/expect/language/flatten_test_none_multi.js

+dart_library.library('language/flatten_test_none_multi', null, /* Imports */[
+  'dart_sdk'
+], function load__flatten_test_none_multi(exports, dart_sdk) {
+  'use strict';
+  const core = dart_sdk.core;
+  const async = dart_sdk.async;
+  const dart = dart_sdk.dart;
+  const dartx = dart_sdk.dartx;
+  const flatten_test_none_multi = Object.create(null);
+  let Derived = () => (Derived = dart.constFn(flatten_test_none_multi.Derived$()))();
+  let FixedPoint = () => (FixedPoint = dart.constFn(flatten_test_none_multi.FixedPoint$()))();
+  let VoidTodynamic = () => (VoidTodynamic = dart.constFn(dart.definiteFunctionType(dart.dynamic, [])))();
+  flatten_test_none_multi.Derived$ = dart.generic(T => {
+    let FutureOfT = () => (FutureOfT = dart.constFn(async.Future$(T)))();
+    const Derived = dart.callableClass(function Derived(...args) {
+      const self = this;
+      function call(...args) {
+        return self.call.apply(self, args);
+      }
+      call.__proto__ = this.__proto__;
+      call.new.apply(call, args);
+      return call;
+    }, class Derived extends core.Object {
+      noSuchMethod(invocation) {
+        return super.noSuchMethod(invocation);
+      }
+    });
+    dart.addTypeTests(Derived);
+    Derived[dart.implements] = () => [FutureOfT()];
+    return Derived;
+  });
+  flatten_test_none_multi.Derived = Derived();
+  flatten_test_none_multi.FixedPoint$ = dart.generic(T => {
+    let FixedPointOfT = () => (FixedPointOfT = dart.constFn(flatten_test_none_multi.FixedPoint$(T)))();
+    let FutureOfFixedPointOfT = () => (FutureOfFixedPointOfT = dart.constFn(async.Future$(FixedPointOfT())))();
+    const FixedPoint = dart.callableClass(function FixedPoint(...args) {
+      const self = this;
+      function call(...args) {
+        return self.call.apply(self, args);
+      }
+      call.__proto__ = this.__proto__;
+      call.new.apply(call, args);
+      return call;
+    }, class FixedPoint extends core.Object {
+      noSuchMethod(invocation) {
+        return super.noSuchMethod(invocation);
+      }
+    });
+    dart.addTypeTests(FixedPoint);
+    FixedPoint[dart.implements] = () => [FutureOfFixedPointOfT()];
+    return FixedPoint;
+  });
+  flatten_test_none_multi.FixedPoint = FixedPoint();
+  flatten_test_none_multi.test = function() {
+    return dart.async(function*() {
+    }, dart.dynamic);
+  };
+  dart.fn(flatten_test_none_multi.test, VoidTodynamic());
+  flatten_test_none_multi.main = function() {
+    flatten_test_none_multi.test();
+  };
+  dart.fn(flatten_test_none_multi.main, VoidTodynamic());
+  // Exports:
+  exports.flatten_test_none_multi = flatten_test_none_multi;
+});