Improve microbenchmarks a smidge (#154461)

1. Allow for selective benchmarks to run locally (see README.md)
2. Shuffle the tests; the seed being rotated daily or specified (see
README.md)

dev/benchmarks/microbenchmarks/README.md

@@ -7,6 +7,19 @@ window to see the device logs, then, in a different window, run:
 flutter run -d $DEVICE_ID --profile lib/benchmark_collection.dart
 ```
 
+To run a subset of tests:
+
+```shell
+flutter run -d $DEVICE_ID --profile lib/benchmark_collection.dart --dart-define=tests=foundation/change_notifier_bench.dart,language/sync_star_bench.dart
+```
+
+To specify a seed value for shuffling tests:
+
+```shell
+flutter run -d $DEVICE_ID --profile lib/benchmark_collection.dart --dart-define=seed=12345
+```
+
+
 The results should be in the device logs.
 
 ## Avoid changing names of the benchmarks

dev/benchmarks/microbenchmarks/lib/benchmark_collection.dart

@@ -3,7 +3,9 @@
 // found in the LICENSE file.
 
 import 'dart:io';
+import 'dart:math';
 
+import 'package:args/args.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/scheduler.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -93,9 +95,44 @@ Future<void> main() async {
     ),
   ];
 
-  print('╡ ••• Running microbenchmarks ••• ╞');
+  // Parses the optional compile-time dart variables; we can't have
+  // arguments passed in to main.
+  final ArgParser parser = ArgParser();
+  final List<String> allowed = benchmarks.map((Benchmark e) => e.$1).toList();
+  parser.addMultiOption(
+    'tests',
+    abbr: 't',
+    defaultsTo: allowed,
+    allowed: allowed,
+    help: 'selected tests to run',
+  );
+  parser.addOption(
+    'seed',
+    defaultsTo: '12345',
+    help: 'selects seed to sort tests by',
+  );
+  final List<String> mainArgs = <String>[];
+  const String testArgs = String.fromEnvironment('tests');
+  if (testArgs.isNotEmpty) {
+    mainArgs.addAll(<String>['--tests', testArgs]);
+    print('╡ ••• environment test override: $testArgs ••• ╞');
+  }
+  const String seedArgs = String.fromEnvironment('seed');
+  if (seedArgs.isNotEmpty) {
+    mainArgs.addAll(<String>['--seed', seedArgs]);
+    print('╡ ••• environment seed override: $seedArgs ••• ╞');
+  }
+  final ArgResults results = parser.parse(mainArgs);
+  final List<String> selectedTests = results.multiOption('tests');
 
-  for (final Benchmark mark in benchmarks) {
+  // Shuffle the tests becauase we don't want order dependent tests.
+  // It is the responsibily of the infra to tell us what the seed value is,
+  // in case we want to have the seed stable for some time period.
+  final List<Benchmark> tests = benchmarks.where((Benchmark e) => selectedTests.contains(e.$1)).toList();
+  tests.shuffle(Random(int.parse(results.option('seed')!)));
+
+  print('╡ ••• Running microbenchmarks ••• ╞');
+  for (final Benchmark mark in tests) {
     // Reset the frame policy to default - each test can set it on their own.
     binding.framePolicy = LiveTestWidgetsFlutterBindingFramePolicy.fadePointers;
     print('╡ ••• Running ${mark.$1} ••• ╞');

dev/devicelab/lib/tasks/microbenchmarks.dart

@@ -19,6 +19,10 @@ TaskFunction createMicrobenchmarkTask({
   bool? enableImpeller,
   Map<String, String> environment = const <String, String>{},
 }) {
+
+  // Generate a seed for this test stable around the date.
+  final int seed = DateTime.now().toUtc().subtract(const Duration(hours: 7)).hashCode;
+
   return () async {
     final Device device = await devices.workingDevice;
     await device.unlock();
@@ -43,7 +47,7 @@ TaskFunction createMicrobenchmarkTask({
 
     Future<Map<String, double>> runMicrobench(String benchmarkPath) async {
       Future<Map<String, double>> run() async {
-        print('Running $benchmarkPath');
+        print('Running $benchmarkPath with seed $seed');
 
         final Process flutterProcess = await inDirectory(appDir, () async {
           final List<String> options = <String>[
@@ -55,6 +59,7 @@ TaskFunction createMicrobenchmarkTask({
             if (enableImpeller != null && !enableImpeller) '--no-enable-impeller',
             '-d',
             device.deviceId,
+            '--dart-define=seed=$seed',
             benchmarkPath,
           ];
           return startFlutter(