Update charted to 0.4.8 and roll

packages/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`.
@@ skipping 36 matching lines @@
       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}) {
+  Future<double> measure({int iterations: 10}) async {
     // 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);
-    });
+    await setup();
+    // Warmup for at least 100ms. Discard result.
+    await measureFor(() => warmup(), 100);
+    // Run the benchmark for at least 2000ms.
+    var result = await measureFor(() => exercise(iterations: iterations), 2000);
+    // Tear down the test (unmeasured) and return the result divided by the
+    // number of iterations.
+    await teardown();
+    return result / iterations;
   }
 }