Check in codegen test expectations.

test/codegen/expect/lib/html/mediasource_test.js

+dart_library.library('lib/html/mediasource_test', null, /* Imports */[
+  'dart_sdk',
+  'unittest'
+], function load__mediasource_test(exports, dart_sdk, unittest) {
+  'use strict';
+  const core = dart_sdk.core;
+  const html = dart_sdk.html;
+  const dart = dart_sdk.dart;
+  const dartx = dart_sdk.dartx;
+  const html_individual_config = unittest.html_individual_config;
+  const src__matcher__core_matchers = unittest.src__matcher__core_matchers;
+  const unittest$ = unittest.unittest;
+  const src__matcher__expect = unittest.src__matcher__expect;
+  const mediasource_test = Object.create(null);
+  let dynamicTobool = () => (dynamicTobool = dart.constFn(dart.definiteFunctionType(core.bool, [dart.dynamic])))();
+  let VoidTodynamic = () => (VoidTodynamic = dart.constFn(dart.definiteFunctionType(dart.dynamic, [])))();
+  let VoidTovoid = () => (VoidTovoid = dart.constFn(dart.definiteFunctionType(dart.void, [])))();
+  mediasource_test.main = function() {
+    html_individual_config.useHtmlIndividualConfiguration();
+    let isMediaSource = src__matcher__core_matchers.predicate(dart.fn(x => html.MediaSource.is(x), dynamicTobool()), 'is a MediaSource');
+    unittest$.group('supported', dart.fn(() => {
+      unittest$.test('supported', dart.fn(() => {
+        src__matcher__expect.expect(html.MediaSource[dartx.supported], true);
+      }, VoidTodynamic()));
+    }, VoidTovoid()));
+    unittest$.group('functional', dart.fn(() => {
+      let source = null;
+      if (dart.test(html.MediaSource[dartx.supported])) {
+        source = html.MediaSource.new();
+      }
+      unittest$.test('constructorTest', dart.fn(() => {
+        if (dart.test(html.MediaSource[dartx.supported])) {
+          src__matcher__expect.expect(source, src__matcher__core_matchers.isNotNull);
+          src__matcher__expect.expect(source, isMediaSource);
+        }
+      }, VoidTodynamic()));
+      unittest$.test('media types', dart.fn(() => {
+        if (dart.test(html.MediaSource[dartx.supported])) {
+          src__matcher__expect.expect(html.MediaSource.isTypeSupported('text/html'), false);
+          src__matcher__expect.expect(html.MediaSource.isTypeSupported('video/webm;codecs="vp8,vorbis"'), true);
+        }
+      }, VoidTodynamic()));
+    }, VoidTovoid()));
+  };
+  dart.fn(mediasource_test.main, VoidTodynamic());
+  // Exports:
+  exports.mediasource_test = mediasource_test;
+});