TaskScheduler: Set the current SequenceToken when a Task runs.

base/task_scheduler/task_tracker.h

 // 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.
 
 #ifndef BASE_TASK_SCHEDULER_TASK_TRACKER_H_
 #define BASE_TASK_SCHEDULER_TASK_TRACKER_H_
 
 #include <memory>
 
 #include "base/base_export.h"
 #include "base/callback_forward.h"
 #include "base/macros.h"
 #include "base/metrics/histogram_base.h"
 #include "base/synchronization/waitable_event.h"
 #include "base/task_scheduler/scheduler_lock.h"
+#include "base/task_scheduler/sequence.h"
 #include "base/task_scheduler/task.h"
 #include "base/task_scheduler/task_traits.h"
 
 namespace base {
 namespace internal {
 
 // All tasks go through the scheduler's TaskTracker when they are posted and
 // when they are executed. The TaskTracker enforces shutdown semantics and takes
 // care of tracing and profiling. This class is thread-safe.
 class BASE_EXPORT TaskTracker {
  public:
   TaskTracker();
   ~TaskTracker();
 
   // Synchronously shuts down the scheduler. Once this is called, only tasks
   // posted with the BLOCK_SHUTDOWN behavior will be run. Returns when:
   // - All SKIP_ON_SHUTDOWN tasks that were already running have completed their
   //   execution.
   // - All posted BLOCK_SHUTDOWN tasks have completed their execution.
   // CONTINUE_ON_SHUTDOWN tasks still may be running after Shutdown returns.
   // This can only be called once.
   void Shutdown();
 
   // Informs this TaskTracker that |task| is about to be posted. Returns true if
   // this operation is allowed (|task| should be posted if-and-only-if it is).
   bool WillPostTask(const Task* task);
 
-  // Runs |task| unless the current shutdown state prevents that. WillPostTask()
-  // must have allowed |task| to be posted.
-  void RunTask(const Task* task);
+  // Runs the next Task in |sequence| unless the current shutdown state prevents
+  // that. WillPostTask() must have allowed the Task to be posted.
+  void RunNextTaskInSequence(const Sequence* sequence);
 
   // Returns true once shutdown has started (Shutdown() has been called but
   // might not have returned).
   bool HasShutdownStarted() const;
 
   // Returns true if shutdown has completed (Shutdown() has returned).
   bool IsShutdownComplete() const;
 
   // Causes HasShutdownStarted() to return true. Unlike when Shutdown() returns,
   // IsShutdownComplete() won't return true after this returns. Shutdown()
@@ skipping 36 matching lines @@
   // Number of BLOCK_SHUTDOWN tasks posted during shutdown.
   HistogramBase::Sample num_block_shutdown_tasks_posted_during_shutdown_ = 0;
 
   DISALLOW_COPY_AND_ASSIGN(TaskTracker);
 };
 
 }  // namespace internal
 }  // namespace base
 
 #endif  // BASE_TASK_SCHEDULER_TASK_TRACKER_H_