content: Add task queue manager

content/renderer/scheduler/task_queue_scheduler.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_TASK_QUEUE_SCHEDULER_H_
+#define CONTENT_RENDERER_SCHEDULER_TASK_QUEUE_SCHEDULER_H_
+
+#include "content/renderer/scheduler/task_queue_manager.h"
+
+namespace content {
+
+class TaskQueueScheduler {
+ public:
+  virtual ~TaskQueueScheduler() {}
+
+  // Called once to register the work queues to be scheduled. This function is
+  // called on the main thread.
+  virtual void SetWorkQueues(

[alexclarke, 2014/10/13 10:06:23]

We need a way for the scheduler to query the sequence number for the head task
of each queue and to determine if it's empty.  This feels like it's exposing too
much information - although perhaps it's up to the code to implement
WebTaskQueue / WebTaskQueueProvider to do the right thing?

For reference here's my current implementation of those classes:

class BLINK_PLATFORM_EXPORT WebTaskQueue {
public:
    virtual size_t numTasksQueued() const = 0;

    virtual int headTaskSequenceNum() const = 0;

protected:
    virtual ~WebTaskQueue() {}
};

class BLINK_PLATFORM_EXPORT WebTaskQueueProvider {
public:
    virtual size_t taskQueueCount() const = 0;

    virtual const WebTaskQueue* WebTaskQueueAt(size_t task_queue_index) const =
0;

protected:
    virtual ~WebTaskQueueProvider() {}
};

[Sami, 2014/10/13 18:16:21]

Looks like we can get away with just exposing the task queues as they are in the
new layout.

+      const std::vector<const base::TaskQueue*>& work_queues) = 0;
+
+  // A new task was placed in the incoming task queue |queue|. This function is
+  // called on the posting thread.
+  virtual void DidQueueTask(TaskQueueManager::QueueId queue) = 0;

[alexclarke, 2014/10/13 10:06:23]

Could we get a function to turn these notifications on/off per queue? As far as
I can tell only information about the compositor queue needs to be pushed to the
scheduler, and it's better for the scheduler to pull information about the other
queues as needed.

[Sami, 2014/10/13 18:16:21]

Notifications are gone now.

+
+  // Called to confirm that the given work queue |queue| should be reloaded as
+  // it has become empty. Return true to allow the work queue to be reloaded or
+  // false to keep the work queue empty.
+  //
+  // This function is called on the main thread.
+  virtual bool ShouldReloadWorkQueue(TaskQueueManager::QueueId queue) = 0;

[alexclarke, 2014/10/13 10:06:23]

I'm surprised the scheduler needs to be aware of this.  Under what circumstances
would it not reload the queue?

[Sami, 2014/10/13 18:16:21]

Also gone.

+
+  // Called to choose the work queue from which the next task should be taken
+  // and run. Return true if |out_queue| indicates the queue to service or
+  // false to avoid running any tasks.
+  //
+  // This function is called on the main thread.
+  virtual bool ChooseWorkQueueToService(
+      TaskQueueManager::QueueId* out_queue) = 0;
+};
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_SCHEDULER_TASK_QUEUE_SCHEDULER_H_