Add timing of serialization

pkg/analyzer/lib/src/util/utilities_timing.dart

Index: pkg/analyzer/lib/src/util/utilities_timing.dart
diff --git a/pkg/analyzer/lib/src/util/utilities_timing.dart b/pkg/analyzer/lib/src/util/utilities_timing.dart
new file mode 100644
index 0000000000000000000000000000000000000000..4d07fcd9bbf48dbf4bce8aee067d03ddbf3af0ee
--- /dev/null
+++ b/pkg/analyzer/lib/src/util/utilities_timing.dart
@@ -0,0 +1,39 @@
+// 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 stop() {
+    super.stop();
+    stopCount++;
+  }
+
+  @override
+  void reset() {
+    super.reset();
+    stopCount = 0;
+  }
+}