TaskScheduler: Add internal::GetTaskPriorityForCurrentThread().

base/task_scheduler/task_traits_for_current_thread.cc

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/task_scheduler/task_traits_for_current_thread.h"
+
+#include "base/lazy_instance.h"
+#include "base/threading/thread_local.h"
+
+namespace base {
+namespace internal {
+
+namespace {
+
+LazyInstance<ThreadLocalPointer<const TaskTraits>>::Leaky
+    tls_traits_for_current_thread = LAZY_INSTANCE_INITIALIZER;
+
+}  // namespace
+
+ScopedSetTaskTraitsForCurrentThread::ScopedSetTaskTraitsForCurrentThread(
+    const TaskTraits* traits)

[robliao, 2016/12/01 18:12:01]

Crazy thought. Can this simply be a const TaskTraits& and we store the address
of that?

[fdoray, 2016/12/01 19:16:02]

n/a with TaskPriority

+#if DCHECK_IS_ON()
+    : traits_(traits)
+#endif
+{
+  DCHECK(!GetTaskTraitsForCurrentThread());
+  DCHECK(traits);
+  tls_traits_for_current_thread.Get().Set(traits);
+}
+
+ScopedSetTaskTraitsForCurrentThread::~ScopedSetTaskTraitsForCurrentThread() {
+#if DCHECK_IS_ON()
+  DCHECK_EQ(traits_, GetTaskTraitsForCurrentThread());

[gab, 2016/12/01 18:04:39]

Is this necessary? As long as we DCHECK == null in the constructor and DCHECK !=
null in destructor then it can't be set to anything else?

[fdoray, 2016/12/01 19:16:02]

Not necessary. Do you still want me to remove it with the latest patch set?

+#endif
+  tls_traits_for_current_thread.Get().Set(nullptr);
+}
+
+const TaskTraits* GetTaskTraitsForCurrentThread() {
+  return tls_traits_for_current_thread.Get().Get();
+}
+
+}  // namespace internal
+}  // namespace base