content/blimp: Set up hooks for enabling LTHRemote in the renderer.

blimp/engine/renderer/scheduler.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 BLIMP_ENGINE_RENDERER_SCHEDULER_H_
+#define BLIMP_ENGINE_RENDERER_SCHEDULER_H_
+
+#include "base/macros.h"
+#include "base/memory/weak_ptr.h"
+#include "base/timer/timer.h"
+
+namespace blimp {
+namespace engine {
+
+class SchedulerClient {
+ public:
+  virtual ~SchedulerClient() {}
+
+  // Used to notify the SchedulerClient to synchronously start the renderer's
+  // main frame.
+  virtual void StartMainFrameUpdate() = 0;
+};
+
+// Responsible for scheduling frame updates sent to the client.
+// The Scheduler uses the state of frames sent to the client and the
+// acknowledgements for these frames from the client to make decisions regarding
+// when a frame should be produced on the engine.

[Wez, 2016/10/18 01:49:42]

And how does it communicate that to the rest of the Engine?  Is that via
StartMainFrameUpdate, for example?

[Khushal, 2016/10/18 05:10:04]

Done.

+class Scheduler {
+ public:
+  Scheduler(scoped_refptr<base::SingleThreadTaskRunner> task_runner,
+            SchedulerClient* client);
+  virtual ~Scheduler();
+
+  // Called when the |client| wants to start a frame update on the engine. We
+  // call it the main frame since this corresponds to a request to start the
+  // main frame update for blink.
+  void SetNeedsMainFrame();
+
+  // Called when a frame update is sent to the client.
+  void DidSendFrameUpdateToClient();
+
+  // Called when an Ack is received for a frame sent to the client.
+  void DidReceiveFrameUpdateAck();
+
+  base::TimeTicks next_frame_time() const { return next_frame_time_; }
+
+ protected:
+  // protected for testing.
+  Scheduler(base::TimeDelta frame_delay,
+            scoped_refptr<base::SingleThreadTaskRunner> task_runner,
+            SchedulerClient* client);
+
+ private:
+  void ScheduleMainFrameIfNecessary();
+
+  // Returns true if a main frame update can be started. The Scheduler can not
+  // produce new frames either if there is no request for main frames pending
+  // or we are waiting for an ack for a frame previously sent to the client.
+  bool CanProduceMainFrames() const;
+
+  void StartMainFrame();
+
+  // Set to true if the |client_| has requested us to schedule main frames.
+  bool needs_main_frame_ = false;
+
+  // Set to true if a frame update was sent to the client and the ack is
+  // pending.
+  bool frame_ack_pending_ = false;
+
+  // The time at which the next main frame update can be run.
+  base::TimeTicks next_frame_time_;
+
+  // The delay to use between consecutive frames.
+  base::TimeDelta frame_delay_;
+
+  base::OneShotTimer frame_tick_timer_;
+
+  SchedulerClient* client_;
+
+  DISALLOW_COPY_AND_ASSIGN(Scheduler);
+};
+
+}  // namespace engine
+}  // namespace blimp
+
+#endif  // BLIMP_ENGINE_RENDERER_SCHEDULER_H_