Roll Observatory packages and add a roll script

code_transformers/lib/src/async_benchmark_base.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 code_transformers.src.async_benchmark_base;
-
-import 'dart:async';
-
-/// An adaptation of [BenchmarkBase] from the `benchmark_harness` package that
-/// works for async benchmarks.
-/// TODO(jakemac): Get this merged into `benchmark_harness`.
-class AsyncBenchmarkBase {
-  // Empty constructor.
-  const AsyncBenchmarkBase();
-
-  // The benchmark code.
-  // This function is not used, if both [warmup] and [exercise] are overwritten.
-  Future run() => new Future.value();
-
-  // Runs a short version of the benchmark. By default invokes [run] once.
-  Future warmup() => run();
-
-  // Exercices the benchmark. By default invokes [run] 10 times.
-  Future exercise({int iterations: 10}) {
-    var i = 0;
-    return Future.doWhile(() {
-      if (i >= iterations) return new Future.value(false);
-      i++;
-      return run().then((_) => true);
-    });
-  }
-
-  // Not measured setup code executed prior to the benchmark runs.
-  Future setup() => new Future.value();
-
-  // Not measures teardown code executed after the benchark runs.
-  Future teardown() => new Future.value();
-
-  // Measures the score for this benchmark by executing it repeatedly until
-  // time minimum has been reached.
-  static Future<double> measureFor(Function f, int minimumMillis) {
-    int minimumMicros = minimumMillis * 1000;
-    int iter = 0;
-    Stopwatch watch = new Stopwatch();
-    watch.start();
-    int elapsed = 0;
-    return Future.doWhile(() {
-      if (elapsed > minimumMicros) return new Future.value(false);
-      return f().then((_) {
-        elapsed = watch.elapsedMicroseconds;
-        iter++;
-        return true;
-      });
-    }).then((_) => elapsed / iter);
-  }
-
-  // Measures the average time to call `run` once and returns it.
-  Future<double> measure({int iterations: 10}) {
-    // Unmeasured setup code.
-    return setup().then((_) {
-      // Warmup for at least 100ms. Discard result.
-      return measureFor(() => warmup(), 100);
-    }).then((_) {
-      // Run the benchmark for at least 2000ms.
-      return measureFor(() => exercise(iterations: iterations), 2000);
-    }).then((result) {
-      // Tear down the test (unmeasured) and return the result divided by the
-      // number of iterations.
-      return teardown().then((_) => result / iterations);
-    });
-  }
-}