scheduler: Add support for tracing scheduler state

content/renderer/scheduler/renderer_task_queue_selector.h

Index: content/renderer/scheduler/renderer_task_queue_selector.h
diff --git a/content/renderer/scheduler/renderer_task_queue_selector.h b/content/renderer/scheduler/renderer_task_queue_selector.h
index 6c9655bafa03cd954f8df26788d726290746a3bb..ee4a175cbe95844653343deeed92a75052ee1b75 100644
--- a/content/renderer/scheduler/renderer_task_queue_selector.h
+++ b/content/renderer/scheduler/renderer_task_queue_selector.h
@@ -52,6 +52,7 @@ class RendererTaskQueueSelector : public TaskQueueSelector {
   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.
@@ -61,6 +62,8 @@ class RendererTaskQueueSelector : public TaskQueueSelector {
   // 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.
@@ -71,6 +74,10 @@ class RendererTaskQueueSelector : public TaskQueueSelector {
   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.