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

base/trace_event/trace_event.h

Index: base/trace_event/trace_event.h
diff --git a/base/trace_event/trace_event.h b/base/trace_event/trace_event.h
index 1105429fd8e261495a55a3b86c3fc8b036e8b331..de06c7d4e56805eb1c632c6af2cca6b156d1df9f 100644
--- a/base/trace_event/trace_event.h
+++ b/base/trace_event/trace_event.h
@@ -437,10 +437,12 @@ TRACE_EVENT_API_CLASS_EXPORT extern \
   INTERNAL_TRACE_EVENT_UID(scoped_context)(context);
 
 // Implementation detail: internal macro to trace a task execution with the
-// location where it was posted from.
-#define INTERNAL_TRACE_TASK_EXECUTION(run_function, task)                      \
-  TRACE_EVENT1("toplevel", run_function, "src_info", (task).GetTracingInfo()); \
-  TRACE_HEAP_PROFILER_API_SCOPED_TASK_EXECUTION INTERNAL_TRACE_EVENT_UID(      \
+// location where it was posted from. Additional metadata may optionally be
+// tacked on as well.
+#define INTERNAL_TRACE_TASK_EXECUTION(run_function, task, ...)             \
+  INTERNAL_TRACE_EVENT_ADD_SCOPED("toplevel", run_function, "src_info",    \
+                                  (task).GetTracingInfo(), ##__VA_ARGS__); \
+  TRACE_HEAP_PROFILER_API_SCOPED_TASK_EXECUTION INTERNAL_TRACE_EVENT_UID(  \
       task_event)((task).posted_from.file_name());
 
 namespace trace_event_internal {