Expedite discovery of primary DRM device.

ui/ozone/platform/drm/host/drm_gpu_platform_support_host.cc

Index: ui/ozone/platform/drm/host/drm_gpu_platform_support_host.cc
diff --git a/ui/ozone/platform/drm/host/drm_gpu_platform_support_host.cc b/ui/ozone/platform/drm/host/drm_gpu_platform_support_host.cc
index 75096a0cb8dc615b89ceed60ffcd6e0642afc774..8d10a8b3885782ebb9e81d55eef47fa434669efb 100644
--- a/ui/ozone/platform/drm/host/drm_gpu_platform_support_host.cc
+++ b/ui/ozone/platform/drm/host/drm_gpu_platform_support_host.cc
@@ -103,17 +103,26 @@ bool DrmGpuPlatformSupportHost::IsConnected() {
   return host_id_ >= 0;
 }
 
-void DrmGpuPlatformSupportHost::OnChannelEstablished(
+void DrmGpuPlatformSupportHost::OnGpuProcessLaunched(
     int host_id,
     scoped_refptr<base::SingleThreadTaskRunner> send_runner,
     const base::Callback<void(IPC::Message*)>& send_callback) {
-  TRACE_EVENT1("drm", "DrmGpuPlatformSupportHost::OnChannelEstablished",
+  TRACE_EVENT1("drm", "DrmGpuPlatformSupportHost::OnGpuProcessLaunched",
                "host_id", host_id);
   host_id_ = host_id;
   send_runner_ = send_runner;
   send_callback_ = send_callback;
 
   for (GpuThreadObserver& observer : gpu_thread_observers_)
+    observer.OnGpuProcessLaunched();
+}
+
+void DrmGpuPlatformSupportHost::OnChannelEstablished() {
+  TRACE_EVENT0("drm", "DrmGpuPlatformSupportHost::OnChannelEstablished");
+
+  channel_established_ = true;
+
+  for (GpuThreadObserver& observer : gpu_thread_observers_)
     observer.OnGpuThreadReady();
 
   // The cursor is special since it will process input events on the IO thread
@@ -131,6 +140,7 @@ void DrmGpuPlatformSupportHost::OnChannelDestroyed(int host_id) {
   if (host_id_ == host_id) {
     cursor_->ResetDrmCursorProxy();
     host_id_ = -1;
+    channel_established_ = false;
     send_runner_ = nullptr;
     send_callback_.Reset();
     for (GpuThreadObserver& observer : gpu_thread_observers_)
@@ -148,8 +158,10 @@ bool DrmGpuPlatformSupportHost::OnMessageReceived(const IPC::Message& message) {
   return false;
 }
 
-bool DrmGpuPlatformSupportHost::Send(IPC::Message* message) {
+bool DrmGpuPlatformSupportHost::SendInternal(
+    IPC::Message* message, bool needChannelEstablished) {
   if (IsConnected() &&
+      (!needChannelEstablished || channel_established_) &&
       send_runner_->PostTask(FROM_HERE, base::Bind(send_callback_, message)))

[piman, 2016/10/31 23:45:46]

Note, because you use PostTask here, it is possible that the
OzoneGpuMsg_AddGraphicsDevice will still be happening "too late".

[hshi1, 2016/11/01 01:00:48]

The GpuProcessHost ctor is called from
BrowserGpuMemoryBufferManager::CreateGpuMemoryBufferOnIO() which does not appear
to synchronously send an IPC to GPU process to allocate the buffer. I believe it
queues the IPC on the IO thread, so any IPC queued earlier on the same thread
should precede it.

[hshi1, 2016/11/01 01:04:41]

To further clarify on this: at the time of GpuProcessHost::Init() the IPC
channel to the GPU process is actually still pending open -- i.e.
GpuProcessHost::Send() would not send the message right away, but queue it in
|queued_messages_|. This would guarantee that the AddGraphics message inserted
here is always first in the queue.

Even if we immediately perform the buffer allocation after this, the IPC message
containing the DRM device would still be sent before everything else at
GpuProcessHost::OnChannelConnected().

     return true;
 
@@ -157,6 +169,10 @@ bool DrmGpuPlatformSupportHost::Send(IPC::Message* message) {
   return false;
 }
 
+bool DrmGpuPlatformSupportHost::Send(IPC::Message* message) {
+  return SendInternal(message, true);
+}
+
 // DisplayHost
 void DrmGpuPlatformSupportHost::RegisterHandlerForDrmDisplayHostManager(
     DrmDisplayHostManager* handler) {
@@ -230,7 +246,7 @@ bool DrmGpuPlatformSupportHost::GpuRelinquishDisplayControl() {
 bool DrmGpuPlatformSupportHost::GpuAddGraphicsDevice(
     const base::FilePath& path,
     const base::FileDescriptor& fd) {
-  return Send(new OzoneGpuMsg_AddGraphicsDevice(path, fd));
+  return SendInternal(new OzoneGpuMsg_AddGraphicsDevice(path, fd), false);
 }
 
 bool DrmGpuPlatformSupportHost::GpuRemoveGraphicsDevice(