Implement video frame acknowledgements in the chromoting protocol.

remoting/host/video_scheduler.cc

Index: remoting/host/video_scheduler.cc
diff --git a/remoting/host/video_scheduler.cc b/remoting/host/video_scheduler.cc
index e374c129cdf26fd32ac6f7804016a9f61db61d8e..c88dd80ae4ab88ec20306e29ab4dffe86e67aa72 100644
--- a/remoting/host/video_scheduler.cc
+++ b/remoting/host/video_scheduler.cc
@@ -80,7 +80,8 @@ void VideoScheduler::Start() {
       this, &VideoScheduler::SendKeepAlivePacket));
 
   capture_task_runner_->PostTask(
-      FROM_HERE, base::Bind(&VideoScheduler::StartOnCaptureThread, this));
+      FROM_HERE, base::Bind(&VideoScheduler::StartOnCaptureThread, this,
+                            video_stub_->SupportsAcks()));
 }
 
 void VideoScheduler::Stop() {
@@ -203,7 +204,7 @@ void VideoScheduler::OnMouseCursorPosition(
   NOTREACHED();
 }
 
-void VideoScheduler::StartOnCaptureThread() {
+void VideoScheduler::StartOnCaptureThread(bool acks_supported) {
   DCHECK(capture_task_runner_->BelongsToCurrentThread());
   DCHECK(!capture_scheduler_);
 
@@ -211,7 +212,7 @@ void VideoScheduler::StartOnCaptureThread() {
   capturer_->Start(this);
 
   capture_scheduler_.reset(new CaptureScheduler(
-      base::Bind(&VideoScheduler::CaptureNextFrame, this)));
+      base::Bind(&VideoScheduler::CaptureNextFrame, this), acks_supported));
   capture_scheduler_->Start();
 }
 
@@ -249,6 +250,13 @@ void VideoScheduler::ProcessFrameSentOnCaptureThread() {
     capture_scheduler_->OnFrameSent();
 }
 
+void VideoScheduler::ProcessFrameAckOnCaptureThread() {
+  DCHECK(capture_task_runner_->BelongsToCurrentThread());
+
+  if (capture_scheduler_)
+    capture_scheduler_->OnFrameAck();
+}
+
 // Network thread --------------------------------------------------------------
 
 void VideoScheduler::SendVideoPacket(scoped_ptr<VideoPacket> packet) {
@@ -258,20 +266,32 @@ void VideoScheduler::SendVideoPacket(scoped_ptr<VideoPacket> packet) {
     return;
 
   video_stub_->ProcessVideoPacket(
-      packet.Pass(), base::Bind(&VideoScheduler::OnVideoPacketSent, this));
+      packet.Pass(), base::Bind(&VideoScheduler::OnVideoPacketProgress, this));
 }
 
-void VideoScheduler::OnVideoPacketSent() {
+void VideoScheduler::OnVideoPacketProgress(
+    protocol::VideoStub::PacketProgress progress) {
   DCHECK(network_task_runner_->BelongsToCurrentThread());
 
   if (!video_stub_)
     return;
 
-  keep_alive_timer_->Reset();
-
-  capture_task_runner_->PostTask(
-      FROM_HERE,
-      base::Bind(&VideoScheduler::ProcessFrameSentOnCaptureThread, this));
+  switch (progress) {
+    case protocol::VideoStub::PacketProgress::SENT:
+      keep_alive_timer_->Reset();
+      capture_task_runner_->PostTask(
+          FROM_HERE,
+          base::Bind(&VideoScheduler::ProcessFrameSentOnCaptureThread, this));
+      break;
+
+    case protocol::VideoStub::PacketProgress::DONE:
+      if (video_stub_->SupportsAcks()) {
+        capture_task_runner_->PostTask(
+            FROM_HERE,
+            base::Bind(&VideoScheduler::ProcessFrameAckOnCaptureThread, this));
+      }
+      break;
+  }
 }
 
 void VideoScheduler::SendKeepAlivePacket() {
@@ -282,14 +302,17 @@ void VideoScheduler::SendKeepAlivePacket() {
 
   video_stub_->ProcessVideoPacket(
       make_scoped_ptr(new VideoPacket()),
-      base::Bind(&VideoScheduler::OnKeepAlivePacketSent, this));
+      base::Bind(&VideoScheduler::OnKeepAlivePacketProgress, this));
 }
 
-void VideoScheduler::OnKeepAlivePacketSent() {
+void VideoScheduler::OnKeepAlivePacketProgress(
+    protocol::VideoStub::PacketProgress progress) {
   DCHECK(network_task_runner_->BelongsToCurrentThread());
 
-  if (keep_alive_timer_)
+  if (progress == protocol::VideoStub::PacketProgress::SENT &&
+      keep_alive_timer_) {
     keep_alive_timer_->Reset();
+  }
 }
 
 void VideoScheduler::SendCursorShape(