Check in codegen test expectations.

test/codegen/expect/language/mixin_issue10216_test.js

+dart_library.library('language/mixin_issue10216_test', null, /* Imports */[
+  'dart_sdk',
+  'expect'
+], function load__mixin_issue10216_test(exports, dart_sdk, expect) {
+  'use strict';
+  const core = dart_sdk.core;
+  const _interceptors = dart_sdk._interceptors;
+  const dart = dart_sdk.dart;
+  const dartx = dart_sdk.dartx;
+  const expect$ = expect.expect;
+  const mixin_issue10216_test = Object.create(null);
+  let JSArrayOfA = () => (JSArrayOfA = dart.constFn(_interceptors.JSArray$(mixin_issue10216_test.A)))();
+  let VoidTodynamic = () => (VoidTodynamic = dart.constFn(dart.definiteFunctionType(dart.dynamic, [])))();
+  mixin_issue10216_test.A = class A extends core.Object {
+    foo(x, y) {
+      if (y === void 0) y = null;
+      return dart.str`${x};${y}`;
+    }
+  };
+  dart.setSignature(mixin_issue10216_test.A, {
+    methods: () => ({foo: dart.definiteFunctionType(dart.dynamic, [dart.dynamic], [dart.dynamic])})
+  });
+  mixin_issue10216_test.M1 = class M1 extends core.Object {};
+  mixin_issue10216_test.M2 = class M2 extends core.Object {
+    plain(x) {
+      return dart.str`P ${x}`;
+    }
+    bar(x, y) {
+      if (y === void 0) y = null;
+      return dart.str`${y},${x}`;
+    }
+  };
+  dart.setSignature(mixin_issue10216_test.M2, {
+    methods: () => ({
+      plain: dart.definiteFunctionType(dart.dynamic, [dart.dynamic]),
+      bar: dart.definiteFunctionType(dart.dynamic, [dart.dynamic], [dart.dynamic])
+    })
+  });
+  mixin_issue10216_test.M3 = class M3 extends core.Object {};
+  mixin_issue10216_test.B = class B extends dart.mixin(mixin_issue10216_test.A, mixin_issue10216_test.M1, mixin_issue10216_test.M2, mixin_issue10216_test.M3) {};
+  mixin_issue10216_test.makeB = function() {
+    return mixin_issue10216_test.B.as(JSArrayOfA().of([new mixin_issue10216_test.A(), new mixin_issue10216_test.B()])[dartx.last]);
+  };
+  dart.fn(mixin_issue10216_test.makeB, VoidTodynamic());
+  mixin_issue10216_test.main = function() {
+    let b = mixin_issue10216_test.makeB();
+    expect$.Expect.equals('1;2', dart.dsend(b, 'foo', 1, 2));
+    expect$.Expect.equals('2;null', dart.dsend(b, 'foo', 2));
+    expect$.Expect.equals('P 3', dart.dsend(b, 'plain', 3));
+    expect$.Expect.equals('100,4', dart.dsend(b, 'bar', 4, 100));
+    expect$.Expect.equals('null,5', dart.dsend(b, 'bar', 5));
+  };
+  dart.fn(mixin_issue10216_test.main, VoidTodynamic());
+  // Exports:
+  exports.mixin_issue10216_test = mixin_issue10216_test;
+});