Add ExecutionMode/SequenceToken and TaskPriority as arguments of TaskScheduler tasks in tracing

base/task_scheduler/task_tracker.cc

Index: base/task_scheduler/task_tracker.cc
diff --git a/base/task_scheduler/task_tracker.cc b/base/task_scheduler/task_tracker.cc
index 1d28f2dab0ba95d944a0679641f96d97cc04a635..8d7b5afc02da5636a460a27cba30ebddc59a4533 100644
--- a/base/task_scheduler/task_tracker.cc
+++ b/base/task_scheduler/task_tracker.cc
@@ -8,7 +8,9 @@
 
 #include "base/callback.h"
 #include "base/debug/task_annotator.h"
+#include "base/json/json_writer.h"
 #include "base/logging.h"
+#include "base/memory/ptr_util.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/sequence_token.h"
 #include "base/synchronization/condition_variable.h"
@@ -16,12 +18,82 @@
 #include "base/threading/thread_restrictions.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "base/trace_event/trace_event.h"
+#include "base/trace_event/trace_event_impl.h"
+#include "base/values.h"
 
 namespace base {
 namespace internal {
 
 namespace {
 
+// An immutable copy of a scheduler task's info required by tracing.
+class TaskTracingInfo : public trace_event::ConvertableToTraceFormat {
+ public:
+  TaskTracingInfo(const TaskTraits& task_traits,
+                  ExecutionMode execution_mode,
+                  const SequenceToken& sequence_token)
+      : task_traits_(task_traits),
+        execution_mode_(execution_mode),
+        sequence_token_(sequence_token) {}
+
+  // Overridden from trace_event::ConvertableToTraceFormat:
+  void AppendAsTraceFormat(std::string* out) const override;
+
+ private:
+  const TaskTraits task_traits_;
+  const ExecutionMode execution_mode_;
+  const SequenceToken sequence_token_;
+
+  DISALLOW_COPY_AND_ASSIGN(TaskTracingInfo);
+};
+
+void TaskTracingInfo::AppendAsTraceFormat(std::string* out) const {
+  DictionaryValue dict;
+
+  bool task_scheduler_tracing_enabled = false;
+  TRACE_EVENT_CATEGORY_GROUP_ENABLED(
+      TRACE_DISABLED_BY_DEFAULT("taskscheduler"),
+      &task_scheduler_tracing_enabled);
+  if (task_scheduler_tracing_enabled) {
+    const char* priority_str = nullptr;
+    switch (task_traits_.priority()) {
+      case TaskPriority::BACKGROUND:
+        priority_str = "BACKGROUND";
+        break;
+      case TaskPriority::USER_VISIBLE:
+        priority_str = "USER_VISIBLE";
+        break;
+      case TaskPriority::USER_BLOCKING:
+        priority_str = "USER_BLOCKING";
+        break;
+    }
+    dict.SetString("TaskPriority", priority_str);
+
+    const char* execution_mode_str = nullptr;
+    switch (execution_mode_) {
+      case ExecutionMode::PARALLEL:
+        execution_mode_str = "PARALLEL";
+        break;
+      case ExecutionMode::SEQUENCED:
+        execution_mode_str = "SEQUENCED";
+        break;
+      case ExecutionMode::SINGLE_THREADED:
+        execution_mode_str = "SINGLE_THREADED";
+        break;
+    }
+    dict.SetString("ExecutionMode", execution_mode_str);
+
+    if (execution_mode_ != ExecutionMode::PARALLEL)
+      dict.SetString("SequenceToken", sequence_token_.ToString());
+  }
+
+  // Even when the taskscheduler tracing category is disabled, a valid (empty)
+  // JSON object still needs to be emitted.
+  std::string tmp;
+  JSONWriter::Write(dict, &tmp);
+  out->append(tmp);
+}
+
 const char kQueueFunctionName[] = "base::PostTask";
 
 // This name conveys that a Task is run by the task scheduler without revealing
@@ -201,7 +273,15 @@ bool TaskTracker::RunTask(const Task* task,
             new ThreadTaskRunnerHandle(task->single_thread_task_runner_ref));
       }
 
-      TRACE_TASK_EXECUTION(kRunFunctionName, *task);
+      ExecutionMode execution_mode =
+          task->single_thread_task_runner_ref
+              ? ExecutionMode::SINGLE_THREADED
+              : (task->sequenced_task_runner_ref ? ExecutionMode::SEQUENCED
+                                                 : ExecutionMode::PARALLEL);
+
+      TRACE_TASK_EXECUTION1(kRunFunctionName, *task, "TaskSchedulerInfo",
+                            MakeUnique<TaskTracingInfo>(
+                                task->traits, execution_mode, sequence_token));
 
       debug::TaskAnnotator task_annotator;
       task_annotator.RunTask(kQueueFunctionName, *task);