DevTools: Make sure RunMicrotasks event is nested into RunTask.

BUG=953914

Change-Id: Ifd1a96df53a3634ce192016c12f6371cf648ad58
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1572937Reviewed-by: Paul Irish <paulirish@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Commit-Queue: Alexei Filippov <alph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#652178}

base/task/common/task_annotator.cc

@@ -78,11 +78,6 @@ void TaskAnnotator::RunTask(const char* trace_event_name,
       TRACE_DISABLED_BY_DEFAULT("toplevel.flow"), trace_event_name,
       TRACE_ID_MANGLE(GetTaskTraceID(*pending_task)), TRACE_EVENT_FLAG_FLOW_IN);
 
-  // Trace-parsing tools (DevTools, Lighthouse, etc) consume this event
-  // to determine long tasks.
-  // See https://crbug.com/681863 and https://crbug.com/874982
-  TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("devtools.timeline"), "RunTask");
-
   // Before running the task, store the task backtrace with the chain of
   // PostTasks that resulted in this call and deliberately alias it to ensure
   // it is on the stack if the task crashes. Be careful not to assume that the

base/task/sequence_manager/thread_controller_impl.cc

@@ -182,6 +182,12 @@ void ThreadControllerImpl::DoWork(WorkType work_type) {
       // Trace events should finish before we call DidRunTask to ensure that
       // SequenceManager trace events do not interfere with them.
       TRACE_TASK_EXECUTION("ThreadControllerImpl::RunTask", *task);
+
+      // Trace-parsing tools (DevTools, Lighthouse, etc) consume this event
+      // to determine long tasks.
+      // See https://crbug.com/681863 and https://crbug.com/874982
+      TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("devtools.timeline"), "RunTask");
+
       task_annotator_.RunTask("SequenceManager RunTask", &*task);
     }
 

base/task/sequence_manager/thread_controller_with_message_pump_impl.cc

@@ -349,6 +349,11 @@ TimeDelta ThreadControllerWithMessagePumpImpl::DoWorkImpl(
 
     work_id_provider_->IncrementWorkId();
 
+    // Trace-parsing tools (DevTools, Lighthouse, etc) consume this event
+    // to determine long tasks.
+    // See https://crbug.com/681863 and https://crbug.com/874982
+    TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("devtools.timeline"), "RunTask");
+
     {
       // Trace events should finish before we call DidRunTask to ensure that
       // SequenceManager trace events do not interfere with them.

third_party/blink/web_tests/http/tests/devtools/tracing/timeline-js/timeline-microtasks-expected.txt

-Checks the RunMicrotasks event is emitted.
+Checks the RunMicrotasks event is emitted and nested into RunTask.
 
 RunMicrotasks Properties:
 {
@@ -9,4 +9,5 @@ RunMicrotasks Properties:
     startTime : <number>
     type : "RunMicrotasks"
 }
+Microtask event is nested into Task event: true
 

third_party/blink/web_tests/http/tests/devtools/tracing/timeline-js/timeline-microtasks.js

@@ -3,7 +3,7 @@
 // found in the LICENSE file.
 
 (async function() {
-  TestRunner.addResult(`Checks the RunMicrotasks event is emitted.\n`);
+  TestRunner.addResult(`Checks the RunMicrotasks event is emitted and nested into RunTask.\n`);
   await TestRunner.loadModule('performance_test_runner');
   await TestRunner.showPanel('timeline');
   await TestRunner.evaluateInPagePromise(`
@@ -27,8 +27,15 @@
   `);
 
   await PerformanceTestRunner.invokeAsyncWithTimeline('performActions');
-  const event = PerformanceTestRunner.mainTrackEvents().find(
+
+  const microTaskEvent = PerformanceTestRunner.mainTrackEvents().find(
       e => e.name === TimelineModel.TimelineModel.RecordType.RunMicrotasks);
-  PerformanceTestRunner.printTraceEventProperties(event);
+  PerformanceTestRunner.printTraceEventProperties(microTaskEvent);
+  const nested = PerformanceTestRunner.mainTrackEvents()
+      .filter(e => e.name === TimelineModel.TimelineModel.RecordType.Task)
+      .some(e => e.startTime <= microTaskEvent.startTime && microTaskEvent.endTime <= e.endTime);
+
+  TestRunner.addResult(`Microtask event is nested into Task event: ${nested}`);
+
   TestRunner.completeTest();
 })();