Add Timer implementation for dart2js. Also moves tests to appropriate location.

lib/isolate/dart2js/timer_provider.dart

+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+
+// We don't want to import the DOM library just because of window.setTimeout,
+// so we reconstruct the Window class here. The only conflict that could happen
+// with the other DOMWindow class would be because of subclasses.
+// Currently, none of the two Dart classes have subclasses.
+typedef void _TimeoutHandler();
+
+class _Window native "@*DOMWindow" {
+  int setTimeout(_TimeoutHandler handler, int timeout) native;
+  int setInterval(_TimeoutHandler handler, int timeout) native;
+}
+
+_Window get _window() =>
+  JS('bool', 'typeof window != "undefined"') ? JS('_Window', 'window') : null;
+
+class _Timer implements Timer {
+  final bool _once;
+  int _handle;
+
+  _Timer(int milliSeconds, void callback(Timer timer))
+      : _once = true {
+    _handle = _window.setTimeout(() => callback(this), milliSeconds);
+  }
+
+  _Timer.repeating(int milliSeconds, void callback(Timer timer))
+      : _once = false {
+    _handle = _window.setInterval(() => callback(this), milliSeconds);
+  }
+
+  void cancel() {
+    if (_once) {
+      _window.clearTimeout(_handle);
+    } else {
+      _window.clearInterval(_handle);
+    }
+  }
+}
+
+Timer _timerFactory(int millis, void callback(Timer timer), bool repeating) =>
+  repeating ? new _Timer.repeating(millis, callback)
+            : new _Timer(millis, callback);