TaskScheduler: Create UpdateableSequencedTaskRunner class to control access to UpdatePriority()

Bug: 889029
Change-Id: Ib8e3967d73a0844ba0d0a9ddb318168e0de1594d
Reviewed-on: https://chromium-review.googlesource.com/c/1349459
Commit-Queue: François Doray <fdoray@chromium.org>
Reviewed-by: François Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611339}

base/BUILD.gn

@@ -984,6 +984,7 @@ jumbo_component("base") {
     "tuple.h",
     "unguessable_token.cc",
     "unguessable_token.h",
+    "updateable_sequenced_task_runner.h",
     "value_conversions.cc",
     "value_conversions.h",
     "value_iterators.cc",

base/task/task_scheduler/scheduler_sequenced_task_runner.h

@@ -11,21 +11,22 @@
 #include "base/task/task_scheduler/scheduler_task_runner_delegate.h"
 #include "base/task/task_scheduler/sequence.h"
 #include "base/task/task_traits.h"
-#include "base/task_runner.h"
 #include "base/time/time.h"
+#include "base/updateable_sequenced_task_runner.h"
 
 namespace base {
 namespace internal {
 
 // A task runner that runs tasks in sequence.
-class BASE_EXPORT SchedulerSequencedTaskRunner : public SequencedTaskRunner {
+class BASE_EXPORT SchedulerSequencedTaskRunner
+    : public UpdateableSequencedTaskRunner {
  public:
   // Constructs a SchedulerSequencedTaskRunner which can be used to post tasks.
   SchedulerSequencedTaskRunner(
       const TaskTraits& traits,
       SchedulerTaskRunnerDelegate* scheduler_task_runner_delegate);
 
-  // SequencedTaskRunner:
+  // UpdateableSequencedTaskRunner:
   bool PostDelayedTask(const Location& from_here,
                        OnceClosure closure,
                        TimeDelta delay) override;
@@ -36,13 +37,11 @@ class BASE_EXPORT SchedulerSequencedTaskRunner : public SequencedTaskRunner {
 
   bool RunsTasksInCurrentSequence() const override;
 
+  void UpdatePriority(TaskPriority priority) override;
+
  private:
   ~SchedulerSequencedTaskRunner() override;
 
-  // Updates the priority for tasks posted through this TaskRunner to
-  // |priority|.
-  void UpdatePriority(TaskPriority priority);
-
   SchedulerTaskRunnerDelegate* const scheduler_task_runner_delegate_;
 
   // Sequence for all Tasks posted through this TaskRunner.

base/updateable_sequenced_task_runner.h

+// Copyright 2018 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.
+
+#ifndef BASE_UPDATEABLE_SEQUENCED_TASK_RUNNER_H_
+#define BASE_UPDATEABLE_SEQUENCED_TASK_RUNNER_H_
+
+#include "base/sequenced_task_runner.h"
+#include "base/task/task_traits.h"
+
+namespace base {
+
+// A SequencedTaskRunner whose posted tasks' priorities can be updated.
+class BASE_EXPORT UpdateableSequencedTaskRunner : public SequencedTaskRunner {
+ public:
+  // Updates the priority for tasks posted through this TaskRunner to
+  // |priority|.
+  virtual void UpdatePriority(TaskPriority priority) = 0;
+
+ protected:
+  UpdateableSequencedTaskRunner() = default;
+  ~UpdateableSequencedTaskRunner() override = default;
+
+  DISALLOW_COPY_AND_ASSIGN(UpdateableSequencedTaskRunner);
+};
+
+}  // namespace base
+
+#endif  // BASE_UPDATEABLE_SEQUENCED_TASK_RUNNER_H_