Add a test for spawning DOM isolate from a pure one.

tests/html/dom_isolates_test.dart

Index: tests/html/dom_isolates_test.dart
diff --git a/tests/html/dom_isolates_test.dart b/tests/html/dom_isolates_test.dart
index ed36360ef066c0b5cce7d4adda7953ebfc305f9b..7ce1386c25aa2ef3d63fe9509a02c81375602c4b 100644
--- a/tests/html/dom_isolates_test.dart
+++ b/tests/html/dom_isolates_test.dart
@@ -8,7 +8,7 @@ import '../../pkg/unittest/lib/html_config.dart';
 import 'dart:html';
 import 'dart:isolate';
 
-isolateMain() {
+childDomIsolate() {
   port.receive((msg, replyTo) {
     if (msg != 'check') {
       replyTo.send('wrong msg: $msg');
@@ -18,8 +18,8 @@ isolateMain() {
   });
 }
 
-isolateMainTrampoline() {
-  final future = spawnDomFunction(isolateMain);
+trampolineIsolate() {
+  final future = spawnDomFunction(childDomIsolate);
   port.receive((msg, parentPort) {
     future.then((childPort) {
       childPort.call(msg).then((response) {
@@ -30,29 +30,28 @@ isolateMainTrampoline() {
   });
 }
 
-dummy() => print("Bad invocation of top-level function");
+dummy() => print('Bad invocation of top-level function');
 
 main() {
   useHtmlConfiguration();
 
   test('Simple DOM isolate test', () {
-    spawnDomFunction(isolateMain).then((sendPort) {
-      sendPort.call('check').then(
-        expectAsync1((msg) {
-          expect(msg, equals('${window.location}'));
-        }));
+    spawnDomFunction(childDomIsolate).then((sendPort) {
+      expect(sendPort.call('check'), completion('${window.location}'));
     });
   });
 
   test('Nested DOM isolates test', () {
-    spawnDomFunction(isolateMainTrampoline).then((sendPort) {
-      sendPort.call('check').then(
-        expectAsync1((msg) {
-          expect(msg, equals('${window.location}'));
-        }));
+    spawnDomFunction(trampolineIsolate).then((sendPort) {
+      expect(sendPort.call('check'), completion('${window.location}'));
     });
   });
 
+  test('Spawn DOM isolate from pure', () {
+    expect(spawnFunction(trampolineIsolate).call('check'),
+           completion('${window.location}'));
+  });
+
   test('Not function', () {
       expect(() => spawnDomFunction(42), throws);
   });
@@ -64,7 +63,7 @@ main() {
 
   test('Masked local function', () {
     var local = 42;
-    dummy() => print("Bad invocation of local function: $local");
+    dummy() => print('Bad invocation of local function: $local');
     expect(() => spawnDomFunction(dummy), throws);
   });
 }