Roll Observatory packages and add a roll script

packages/petitparser/test/json_benchmark.dart

+library petitparser.test.json_benchmark;
+
+import 'package:petitparser/json.dart';
+
+import 'dart:convert';
+
+double benchmark(Function function, [int warmup = 1000, int milliseconds = 5000]) {
+  var count = 0;
+  var elapsed = 0;
+  var watch = new Stopwatch();
+  while (warmup-- > 0) {
+    function();
+  }
+  watch.start();
+  while (elapsed < milliseconds) {
+    function();
+    elapsed = watch.elapsedMilliseconds;
+    count++;
+  }
+  return elapsed / count;
+}
+
+const jsonEvent = '{"type": "change", "eventPhase": 2, "bubbles": true, "cancelable": true, '
+    '"timeStamp": 0, "CAPTURING_PHASE": 1, "AT_TARGET": 2, "BUBBLING_PHASE": 3, "isTrusted": '
+    'true, "MOUSEDOWN": 1, "MOUSEUP": 2, "MOUSEOVER": 4, "MOUSEOUT": 8, "MOUSEMOVE": 16, '
+    '"MOUSEDRAG": 32, "CLICK": 64, "DBLCLICK": 128, "KEYDOWN": 256, "KEYUP": 512, "KEYPRESS": '
+    '1024, "DRAGDROP": 2048, "FOCUS": 4096, "BLUR": 8192, "SELECT": 16384, "CHANGE": 32768, '
+    '"RESET": 65536, "SUBMIT": 131072, "SCROLL": 262144, "LOAD": 524288, "UNLOAD": 1048576, '
+    '"XFER_DONE": 2097152, "ABORT": 4194304, "ERROR": 8388608, "LOCATE": 16777216, "MOVE": '
+    '33554432, "RESIZE": 67108864, "FORWARD": 134217728, "HELP": 268435456, "BACK": 536870912, '
+    '"TEXT": 1073741824, "ALT_MASK": 1, "CONTROL_MASK": 2, "SHIFT_MASK": 4, "META_MASK": 8}';
+
+final JsonParser json = new JsonParser();
+
+dynamic native(String input) => JSON.decode(input);
+dynamic custom(String input) => json.parse(input).value;
+
+void main() {
+  var nativeResult = native(jsonEvent);
+  var customResult = custom(jsonEvent);
+
+  if (nativeResult.toString() != customResult.toString()) {
+    print('Results not matching!');
+    print('  Native: $nativeResult');
+    print('  Custom: $customResult');
+    return;
+  }
+
+  var nativeTime = benchmark(() => native(jsonEvent));
+  var customTime = benchmark(() => custom(jsonEvent));
+  var ratio = customTime / nativeTime;
+
+  print('Slowdown: ${ratio.toStringAsFixed(1)}');
+  print('Native: ${nativeTime.toStringAsFixed(6)}');
+  print('Custom: ${customTime.toStringAsFixed(6)}');
+}