Add tests for timers in background isolates in Dartium.

tests/html/async_spawnuri_test.dart

Index: tests/html/async_spawnuri_test.dart
diff --git a/tests/html/async_spawnuri_test.dart b/tests/html/async_spawnuri_test.dart
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+++ b/tests/html/async_spawnuri_test.dart
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+library async_spawnuri_test;
+
+import 'package:unittest/unittest.dart';
+import 'package:unittest/html_config.dart';
+
+import 'dart:async';
+import 'dart:isolate';
+import 'dart:html';
+
+// OtherScripts=async_oneshot.dart async_periodictimer.dart async_cancellingisolate.dart
+main() {
+  useHtmlConfiguration();
+
+  test('one shot timer in pure isolate', () {
+    var response = new ReceivePort();
+    var remote = Isolate.spawnUri(Uri.parse('async_oneshot.dart'), 
+                               ['START'], response.sendPort);
+    remote.catchError((x) => expect("Error in oneshot isolate", x));
+    expect(remote.then((_) => response.first), completion('DONE'));
+  });
+
+  test('periodic timer in pure isolate', () {
+    var response = new ReceivePort();
+    var remote = Isolate.spawnUri(Uri.parse('async_periodictimer.dart'), 
+                               ['START'], response.sendPort);
+    remote.catchError((x) => expect("Error in periodic timer isolate", x));
+    expect(remote.then((_) => response.first), completion('DONE'));
+  });
+
+  test('cancellation in pure isolate', () {
+    var response = new ReceivePort();
+    var remote = Isolate.spawnUri(Uri.parse('async_cancellingisolate.dart'), 
+                               ['START'], response.sendPort);
+    remote.catchError((x) => expect("Error in cancelling isolate", x));
+    expect(remote.then((_) => response.first), completion('DONE'));
+  });
+}