Replace base::Callback with base::OnceCallback in base::PendingTask

base/debug/task_annotator.cc

Index: base/debug/task_annotator.cc
diff --git a/base/debug/task_annotator.cc b/base/debug/task_annotator.cc
index 2747d63c2bf29aa3d356c8c750ff3784b943e66f..437d69a7f8be025b17dabe29adb12c7dedc63816 100644
--- a/base/debug/task_annotator.cc
+++ b/base/debug/task_annotator.cc
@@ -28,34 +28,32 @@ void TaskAnnotator::DidQueueTask(const char* queue_function,
 }
 
 void TaskAnnotator::RunTask(const char* queue_function,
-                            const PendingTask& pending_task) {
-  ScopedTaskRunActivity task_activity(pending_task);
+                            PendingTask* pending_task) {
+  ScopedTaskRunActivity task_activity(*pending_task);
 
   tracked_objects::TaskStopwatch stopwatch;
   stopwatch.Start();
   tracked_objects::Duration queue_duration =
-      stopwatch.StartTime() - pending_task.EffectiveTimePosted();
+      stopwatch.StartTime() - pending_task->EffectiveTimePosted();
 
-  TRACE_EVENT_WITH_FLOW1(TRACE_DISABLED_BY_DEFAULT("toplevel.flow"),
-                          queue_function,
-                          TRACE_ID_MANGLE(GetTaskTraceID(pending_task)),
-                          TRACE_EVENT_FLAG_FLOW_IN,
-                          "queue_duration",
-                          queue_duration.InMilliseconds());
+  TRACE_EVENT_WITH_FLOW1(
+      TRACE_DISABLED_BY_DEFAULT("toplevel.flow"), queue_function,
+      TRACE_ID_MANGLE(GetTaskTraceID(*pending_task)), TRACE_EVENT_FLAG_FLOW_IN,
+      "queue_duration", queue_duration.InMilliseconds());
 
   // Before running the task, store the program counter where it was posted
   // and deliberately alias it to ensure it is on the stack if the task
   // crashes. Be careful not to assume that the variable itself will have the
   // expected value when displayed by the optimizer in an optimized build.
   // Look at a memory dump of the stack.
-  const void* program_counter = pending_task.posted_from.program_counter();
+  const void* program_counter = pending_task->posted_from.program_counter();
   debug::Alias(&program_counter);
 
-  pending_task.task.Run();
+  std::move(pending_task->task).Run();

[fdoray, 2016/10/06 17:37:22]

It's annoying that Run() can only be called on an l-value. What would have
prevented Run() from being implemented like this?

  R Run(Args... args) {
    CallbackType& cb = static_cast<CallbackType&>(*this);
    PolymorphicInvoke f =
        reinterpret_cast<PolymorphicInvoke>(cb.polymorphic_invoke());

    // Move |bind_state| to ensure that it is deleted after the invocation. It's
    // not safe to touch |this| after the invocation, since running the bound
    // function may destroy |this|.
    scoped_refptr<BindStateBase> bind_state = std::move(cb.bind_state_);

    return f(bind_state.get(), std::forward<Args>(args)...);
  }

[tzik, 2016/10/13 05:58:04]

Per discussion on the mail thread:
In the new semantics, OnceClosure::Run() consumes the closure object itself and
clears itself. So we'd like the caller to mark it by std::move() explicitly.

 
   stopwatch.Stop();
-  tracked_objects::ThreadData::TallyRunOnNamedThreadIfTracking(
-      pending_task, stopwatch);
+  tracked_objects::ThreadData::TallyRunOnNamedThreadIfTracking(*pending_task,
+                                                               stopwatch);
 }
 
 uint64_t TaskAnnotator::GetTaskTraceID(const PendingTask& task) const {