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..8b3bafba0ce8fce0ccd8afe4681b18295f2c3f23 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
@@ -100,20 +100,28 @@ void DrmGpuPlatformSupportHost::RemoveGpuThreadObserver(
 }
 
 bool DrmGpuPlatformSupportHost::IsConnected() {
-  return host_id_ >= 0;
+  return host_id_ >= 0 && channel_established_;
 }
 
-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 +139,7 @@ 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_)
@@ -230,7 +239,21 @@ bool DrmGpuPlatformSupportHost::GpuRelinquishDisplayControl() {
 bool DrmGpuPlatformSupportHost::GpuAddGraphicsDevice(
     const base::FilePath& path,
     const base::FileDescriptor& fd) {
-  return Send(new OzoneGpuMsg_AddGraphicsDevice(path, fd));
+  IPC::Message* message = new OzoneGpuMsg_AddGraphicsDevice(path, fd);
+
+  // This function may be called from two places:
+  // - DrmDisplayHostManager::OnGpuProcessLaunched() invoked synchronously
+  //   by GpuProcessHost::Init() on IO thread, which is the same thread as
+  //   |send_runner_|. In this case we can synchronously send the IPC;
+  // - DrmDisplayHostManager::OnAddGraphicsDevice() on UI thread. In this
+  //   case we need to post the send task to IO thread.
+  if (send_runner_ && send_runner_->BelongsToCurrentThread()) {
+    DCHECK(!send_callback_.is_null());
+    send_callback_.Run(message);
+    return true;
+  }
+
+  return Send(message);
 }
 
 bool DrmGpuPlatformSupportHost::GpuRemoveGraphicsDevice(