Add observatory_pub_packages snapshot to third_party

observatory_pub_packages/polymer/src/job.dart

+// Copyright (c) 2013, 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.
+
+part of polymer;
+
+/// Like [Timer] but can be restarted, and if no duration is supplied uses
+/// [window.requestAnimationFrame] instead of a 0-duration timer.
+// TODO(jmesserly): need to find a better name here. Also this feels more like a
+// system level API, but doesn't map exactly to any of our other primitives.
+class PolymerJob {
+  Function _callback;
+  Timer _timer;
+  int _id; // for requestAnimationFrame
+
+  PolymerJob._();
+
+  bool get isScheduled => _timer != null || _id != null;
+
+  /// Starts the job. If the job is already running, it will [stop] first.
+  void start(void callback(), [Duration wait]) {
+    stop();
+    _callback = callback;
+    if (wait == null) {
+      _id = window.requestAnimationFrame((_) => complete());
+    } else {
+      _timer = new Timer(wait, complete);
+    }
+  }
+
+  /// Stops the job. It can be restarted by calling [start] with a new callback.
+  void stop() {
+    if (_id != null) {
+      window.cancelAnimationFrame(_id);
+      _id = null;
+    }
+    if (_timer != null) {
+      _timer.cancel();
+      _timer = null;
+    }
+  }
+
+  /// Synchronously completes the job.
+  void complete() {
+    if (isScheduled) {
+      stop();
+      _callback();
+    }
+  }
+}