Tracing: Add capability to trace the priority of the tasks executed.

Change-Id: I0ab635c48c63ff68a8aeca1d725904d0f4eb56b9
Reviewed-on: https://chromium-review.googlesource.com/1053774Reviewed-by: Alexander Timin <altimin@chromium.org>
Commit-Queue: Farah Charab <farahcharab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#558361}

third_party/blink/renderer/platform/scheduler/main_thread/main_thread_scheduler_impl.cc

@@ -203,6 +203,13 @@ const char* OptionalTaskDescriptionToString(
   return MainThreadTaskQueue::NameForQueueType(desc->queue_type.value());
 }
 
+const char* OptionalTaskPriorityToString(
+    base::Optional<TaskQueue::QueuePriority> priority) {
+  if (!priority)
+    return nullptr;
+  return TaskQueue::PriorityToString(priority.value());
+}
+
 bool IsUnconditionalHighPriorityInputEnabled() {
   return base::FeatureList::IsEnabled(kHighPriorityInput);
 }
@@ -528,6 +535,12 @@ MainThreadSchedulerImpl::MainThreadOnly::MainThreadOnly(
           main_thread_scheduler_impl,
           &main_thread_scheduler_impl->tracing_controller_,
           OptionalTaskDescriptionToString),
+      task_priority_for_tracing(
+          base::nullopt,
+          "Scheduler.TaskPriority",
+          main_thread_scheduler_impl,
+          &main_thread_scheduler_impl->tracing_controller_,
+          OptionalTaskPriorityToString),
       virtual_time_policy(VirtualTimePolicy::kAdvance),
       virtual_time_pause_count(0),
       max_virtual_time_task_starvation_count(0),
@@ -2426,6 +2439,11 @@ void MainThreadSchedulerImpl::OnTaskStarted(MainThreadTaskQueue* queue,
       queue
           ? base::Optional<MainThreadTaskQueue::QueueType>(queue->queue_type())
           : base::nullopt};
+
+  main_thread_only().task_priority_for_tracing =
+      queue
+          ? base::Optional<TaskQueue::QueuePriority>(queue->GetQueuePriority())
+          : base::nullopt;
 }
 
 void MainThreadSchedulerImpl::OnTaskCompleted(
@@ -2445,6 +2463,9 @@ void MainThreadSchedulerImpl::OnTaskCompleted(
                                                       thread_time);
   main_thread_only().task_description_for_tracing = base::nullopt;
 
+  // Unset the state of |task_priority_for_tracing|.
+  main_thread_only().task_priority_for_tracing = base::nullopt;
+
   RecordTaskUkm(queue, task, start, end, thread_time);
 }
 

third_party/blink/renderer/platform/scheduler/main_thread/main_thread_scheduler_impl.h

@@ -19,6 +19,7 @@
 #include "build/build_config.h"
 #include "third_party/blink/public/platform/scheduler/web_main_thread_scheduler.h"
 #include "third_party/blink/renderer/platform/platform_export.h"
+#include "third_party/blink/renderer/platform/scheduler/base/task_queue.h"
 #include "third_party/blink/renderer/platform/scheduler/base/task_time_observer.h"
 #include "third_party/blink/renderer/platform/scheduler/child/idle_canceled_delayed_task_sweeper.h"
 #include "third_party/blink/renderer/platform/scheduler/child/idle_helper.h"
@@ -723,6 +724,10 @@ class PLATFORM_EXPORT MainThreadSchedulerImpl
     TraceableState<base::Optional<TaskDescriptionForTracing>,
                    kTracingCategoryNameInfo>
         task_description_for_tracing;  // Don't use except for tracing.
+    TraceableState<
+        base::Optional<base::sequence_manager::TaskQueue::QueuePriority>,
+        kTracingCategoryNameInfo>
+        task_priority_for_tracing;  // Only used for tracing.
     base::ObserverList<VirtualTimeObserver> virtual_time_observers;
     base::Time initial_virtual_time;
     base::TimeTicks initial_virtual_time_ticks;