Switch DRM platform to using a separate thread

ui/ozone/platform/drm/gpu/drm_device_manager.cc

Index: ui/ozone/platform/drm/gpu/drm_device_manager.cc
diff --git a/ui/ozone/platform/drm/gpu/drm_device_manager.cc b/ui/ozone/platform/drm/gpu/drm_device_manager.cc
index b01664abb706586b1332aee3d22d82fa6f87a5f0..1448caeb477be5dbd0c0eb97cd97229e58b7fdc5 100644
--- a/ui/ozone/platform/drm/gpu/drm_device_manager.cc
+++ b/ui/ozone/platform/drm/gpu/drm_device_manager.cc
@@ -55,9 +55,6 @@ bool DrmDeviceManager::AddDrmDevice(const base::FilePath& path,
     return false;
   }
 
-  if (io_task_runner_)
-    device->InitializeTaskRunner(io_task_runner_);
-
   if (!primary_device_)
     primary_device_ = device;
 
@@ -78,15 +75,6 @@ void DrmDeviceManager::RemoveDrmDevice(const base::FilePath& path) {
   devices_.erase(it);
 }
 
-void DrmDeviceManager::InitializeIOTaskRunner(
-    const scoped_refptr<base::SingleThreadTaskRunner>& task_runner) {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  DCHECK(!io_task_runner_);
-  io_task_runner_ = task_runner;
-  for (const auto& device : devices_)
-    device->InitializeTaskRunner(io_task_runner_);
-}
-
 void DrmDeviceManager::UpdateDrmDevice(gfx::AcceleratedWidget widget,
                                        const scoped_refptr<DrmDevice>& device) {
   base::AutoLock lock(lock_);