scheduler: Add support for tracing scheduler state

content/renderer/scheduler/renderer_task_queue_selector.h

 // Copyright 2014 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 CONTENT_RENDERER_SCHEDULER_RENDERER_TASK_QUEUE_SELECTOR_H
 #define CONTENT_RENDERER_SCHEDULER_RENDERER_TASK_QUEUE_SELECTOR_H
 
 #include <set>
 
 #include "base/compiler_specific.h"
@@ skipping 37 matching lines @@
   // queues are enabled with normal priority.
   void EnableQueue(size_t queue_index, QueuePriority priority);
 
   // Disable the |queue_index|.
   void DisableQueue(size_t queue_index);
 
   // TaskQueueSelector implementation:
   void RegisterWorkQueues(
       const std::vector<const base::TaskQueue*>& work_queues) override;
   bool SelectWorkQueueToService(size_t* out_queue_index) override;
+  void AsValueInto(base::debug::TracedValue* state) const override;
 
  private:
   // Returns true if queueA contains an older task than queueB.
   static bool IsOlder(const base::TaskQueue* queueA,
                       const base::TaskQueue* queueB);
 
   // Returns the priority which is next after |priority|.
   static QueuePriority NextPriority(QueuePriority priority);
 
+  static const char* PriorityToString(QueuePriority priority);
+
   // Return true if |out_queue_index| indicates the index of the queue with
   // the oldest pending task from the set of queues of |priority|, or
   // false if all queues of that priority are empty.
   bool ChooseOldestWithPriority(QueuePriority priority,
                                 size_t* out_queue_index) const;
 
   // Returns true if |queue_index| is enabled with the given |priority|.
   bool QueueEnabledWithPriority(size_t queue_index,
                                 QueuePriority priority) const;
 
+  // Called whenever the selector chooses a task queue for execution with the
+  // priority |priority|.
+  void DidSelectQueueWithPriority(QueuePriority priority);
+
   // Number of high priority tasks which can be run before a normal priority
   // task should be selected to prevent starvation.
   // TODO(rmcilroy): Check if this is a good value.
   static const size_t kMaxStarvationTasks = 5;
 
   base::ThreadChecker main_thread_checker_;
   std::vector<const base::TaskQueue*> work_queues_;
   std::set<size_t> queue_priorities_[QUEUE_PRIORITY_COUNT];
   size_t starvation_count_;
   DISALLOW_COPY_AND_ASSIGN(RendererTaskQueueSelector);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_SCHEDULER_RENDERER_TASK_QUEUE_SELECTOR_H