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

blimp/engine/renderer/frame_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_FRAME_SCHEDULER_H_
+#define BLIMP_ENGINE_RENDERER_FRAME_SCHEDULER_H_
+
+#include "base/macros.h"
+#include "base/memory/weak_ptr.h"
+#include "base/timer/timer.h"
+
+namespace blimp {
+namespace engine {
+
+class FrameSchedulerClient {
+ public:
+  virtual ~FrameSchedulerClient() {}
+
+  // Used to notify the SchedulerClient to start the requested frame update.
+  // Calling this method marks the completion of the frame update request made
+  // to the scheduler. Any calls to schedule a frame after this will result in
+  // a new frame update.
+  // The frame update must be run synchronously, and if it results in any
+  // content changes sent to the blimp client, the scheduler must be informed
+  // using DidSendFrameUpdateToClient.
+  virtual void StartFrameUpdate() = 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.
+// The caller provides a SchedulerClient to be notified when a frame update
+// should be produced. The SchedulerClient must outlive this class.
+class FrameScheduler {
+ public:
+  FrameScheduler(scoped_refptr<base::SingleThreadTaskRunner> task_runner,
+                 FrameSchedulerClient* client);
+  virtual ~FrameScheduler();
+
+  // Called when the |client| wants to start a frame update on the engine. The
+  // |client| will be asynchronously informed of starting a frame update using

[Wez, 2016/10/25 21:50:09]

nit: "|client->StartFrameUpdate() will be called[-back?] asynchronously when the
scheduler is ready for the next frame to be started."?

[Khushal, 2016/10/26 00:01:40]

Done.

+  // FrameSchedulerClient::StartFrameUpdate.
+  void ScheduleFrameUpdate();
+
+  // Called when a frame update is sent to the client. This must be followed
+  // with a DidReceiveFrameUpdateAck when the frame sent is ack-ed by the
+  // client.

[Wez, 2016/10/25 21:50:09]

Make explicit that this MUST be called from within StartFrameUpdate(), before it
returns, if that is the requirement.  Or, better still, get rid of this and have
StartFrameUpdate() return a bool indicating whether or not it actually sent
anything.

[Khushal, 2016/10/26 00:01:40]

I added a DCHECK to make sure it is only called from StartFrameUpdate. Otherwise
to return the bool from that function I would be doing the same thing in
BlimpRemoteCompositorBridge.

+  void DidSendFrameUpdateToClient();
+
+  // Called when an Ack is received for a frame sent to the client.
+  void DidReceiveFrameUpdateAck();
+
+ protected:
+  // protected for testing.
+  FrameScheduler(base::TimeDelta frame_delay,
+                 scoped_refptr<base::SingleThreadTaskRunner> task_runner,
+                 FrameSchedulerClient* client);
+
+ private:
+  void ScheduleFrameUpdateIfNecessary();
+
+  // Returns true if a frame update can be started. The Scheduler can not
+  // produce new frames either if there is no request for frames pending or we
+  // are waiting for an ack for a frame previously sent to the client.
+  bool ShouldProduceFrameUpdates() const;
+
+  void StartFrameUpdate();
+
+  // Set to true if the |client_| has requested us to schedule frames.
+  bool needs_frame_update_ = 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_;
+
+  FrameSchedulerClient* client_;
+
+  DISALLOW_COPY_AND_ASSIGN(FrameScheduler);
+};
+
+}  // namespace engine
+}  // namespace blimp
+
+#endif  // BLIMP_ENGINE_RENDERER_FRAME_SCHEDULER_H_