disable tracing for non-frame based benchmarks (#54236)

dev/benchmarks/macrobenchmarks/lib/src/web/recorder.dart

@@ -50,6 +50,11 @@ Duration timeAction(VoidCallback action) {
 /// A function that performs asynchronous work.
 typedef AsyncVoidCallback = Future<void> Function();
 
+/// An [AsyncVoidCallback] that doesn't do anything.
+///
+/// This is used just so we don't have to deal with null all over the place.
+Future<void> _dummyAsyncVoidCallback() async {}
+
 /// Runs the benchmark using the given [recorder].
 ///
 /// Notifies about "set up" and "tear down" events via the [setUpAllDidRun]
@@ -61,8 +66,8 @@ class Runner {
   /// All arguments must not be null.
   Runner({
     @required this.recorder,
-    @required this.setUpAllDidRun,
-    @required this.tearDownAllWillRun,
+    this.setUpAllDidRun = _dummyAsyncVoidCallback,
+    this.tearDownAllWillRun = _dummyAsyncVoidCallback,
   });
 
   /// The recorder that will run and record the benchmark.
@@ -95,7 +100,11 @@ class Runner {
 ///
 /// Each benchmark recorder has a [name] and a [run] method at a minimum.
 abstract class Recorder {
-  Recorder._(this.name);
+  Recorder._(this.name, this.isTracingEnabled);
+
+  /// Whether this recorder requires tracing using Chrome's DevTools Protocol's
+  /// "Tracing" API.
+  final bool isTracingEnabled;
 
   /// The name of the benchmark.
   ///
@@ -143,7 +152,7 @@ abstract class Recorder {
 /// }
 /// ```
 abstract class RawRecorder extends Recorder {
-  RawRecorder({@required String name}) : super._(name);
+  RawRecorder({@required String name}) : super._(name, false);
 
   /// The body of the benchmark.
   ///
@@ -188,7 +197,7 @@ abstract class RawRecorder extends Recorder {
 /// }
 /// ```
 abstract class SceneBuilderRecorder extends Recorder {
-  SceneBuilderRecorder({@required String name}) : super._(name);
+  SceneBuilderRecorder({@required String name}) : super._(name, true);
 
   /// Called from [Window.onBeginFrame].
   @mustCallSuper
@@ -306,7 +315,7 @@ abstract class SceneBuilderRecorder extends Recorder {
 /// }
 /// ```
 abstract class WidgetRecorder extends Recorder implements FrameRecorder {
-  WidgetRecorder({@required String name}) : super._(name);
+  WidgetRecorder({@required String name}) : super._(name, true);
 
   /// Creates a widget to be benchmarked.
   ///
@@ -377,7 +386,7 @@ abstract class WidgetRecorder extends Recorder implements FrameRecorder {
 /// performance of frames that render the widget and ignoring the frames that
 /// clear the screen.
 abstract class WidgetBuildRecorder extends Recorder implements FrameRecorder {
-  WidgetBuildRecorder({@required String name}) : super._(name);
+  WidgetBuildRecorder({@required String name}) : super._(name, true);
 
   /// Creates a widget to be benchmarked.
   ///

dev/benchmarks/macrobenchmarks/lib/web_benchmarks.dart

@@ -70,19 +70,14 @@ Future<void> _runBenchmark(String benchmarkName) async {
   }
 
   try {
-    final Runner runner = Runner(
-      recorder: recorderFactory(),
-      setUpAllDidRun: () async {
-        if (!_client.isInManualMode) {
-          await _client.startPerformanceTracing(benchmarkName);
-        }
-      },
-      tearDownAllWillRun: () async {
-        if (!_client.isInManualMode) {
-          await _client.stopPerformanceTracing();
-        }
-      },
-    );
+    final Recorder recorder = recorderFactory();
+    final Runner runner = recorder.isTracingEnabled && !_client.isInManualMode
+      ? Runner(
+          recorder: recorder,
+          setUpAllDidRun: () => _client.startPerformanceTracing(benchmarkName),
+          tearDownAllWillRun: _client.stopPerformanceTracing,
+        )
+      : Runner(recorder: recorder);
 
     final Profile profile = await runner.run();
     if (!_client.isInManualMode) {

dev/devicelab/lib/framework/browser.dart

@@ -282,6 +282,14 @@ class BlinkTraceSummary {
         .toList()
         ..sort((BlinkTraceEvent a, BlinkTraceEvent b) => a.ts - b.ts);
 
+      Exception noMeasuredFramesFound() => Exception(
+        'No measured frames found in benchmark tracing data. This likely '
+        'indicates a bug in the benchmark. For example, the benchmark failed '
+        'to pump enough frames. It may also indicate a change in Chrome\'s '
+        'tracing data format. Check if Chrome version changed recently and '
+        'adjust the parsing code accordingly.',
+      );
+
       // Use the pid from the first "measured_frame" event since the event is
       // emitted by the script running on the process we're interested in.
       //
@@ -290,7 +298,7 @@ class BlinkTraceSummary {
       // sometimes, causing to flakes.
       final BlinkTraceEvent firstMeasuredFrameEvent = events.firstWhere(
         (BlinkTraceEvent event) => event.isBeginMeasuredFrame,
-        orElse: () => null,
+        orElse: () => throw noMeasuredFramesFound(),
       );
 
       if (firstMeasuredFrameEvent == null) {
@@ -330,8 +338,7 @@ class BlinkTraceSummary {
       print('Skipped $skipCount non-measured frames.');
 
       if (frames.isEmpty) {
-        // The benchmark is not measuring frames.
-        return null;
+        throw noMeasuredFramesFound();
       }
 
       // Compute averages and summarize.

dev/devicelab/lib/tasks/web_benchmarks.dart

@@ -65,15 +65,14 @@ Future<TaskResult> runWebBenchmark({ @required bool useCanvasKit }) async {
             server.close();
           }
 
+          // Trace data is null when the benchmark is not frame-based, such as RawRecorder.
+          if (latestPerformanceTrace != null) {
             final BlinkTraceSummary traceSummary = BlinkTraceSummary.fromJson(latestPerformanceTrace);
-
-          // Trace summary can be null if the benchmark is not frame-based, such as RawRecorder.
-          if (traceSummary != null) {
             profile['totalUiFrame.average'] = traceSummary.averageTotalUIFrameTime.inMicroseconds;
             profile['scoreKeys'] ??= <dynamic>[]; // using dynamic for consistency with JSON
             profile['scoreKeys'].add('totalUiFrame.average');
-          }
             latestPerformanceTrace = null;
+          }
           collectedProfiles.add(profile);
           return Response.ok('Profile received');
         } else if (request.requestedUri.path.endsWith('/start-performance-tracing')) {