Roll Observatory packages and add a roll script

analyzer/lib/src/util/utilities_timing.dart

-// Copyright (c) 2014, 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.
-
-library engine.utilities.timing;
-
-/**
- * A `CountedStopwatch` is a [Stopwatch] that counts the number of times the
- * stop method has been invoked.
- */
-class CountedStopwatch extends Stopwatch {
-  /**
-   * The number of times the [stop] method has been invoked.
-   */
-  int stopCount = 0;
-
-  /**
-   * Initialize a newly created stopwatch.
-   */
-  CountedStopwatch();
-
-  /**
-   * The average number of millisecond that were recorded each time the [start]
-   * and [stop] methods were invoked.
-   */
-  int get averageMilliseconds => elapsedMilliseconds ~/ stopCount;
-
-  @override
-  void reset() {
-    super.reset();
-    stopCount = 0;
-  }
-
-  @override
-  void stop() {
-    super.stop();
-    stopCount++;
-  }
-}