Expedite discovery of primary DRM device.

ui/ozone/platform/drm/host/gpu_thread_observer.h

Index: ui/ozone/platform/drm/host/gpu_thread_observer.h
diff --git a/ui/ozone/platform/drm/host/gpu_thread_observer.h b/ui/ozone/platform/drm/host/gpu_thread_observer.h
index 3307dfa8fcbb0f763793ca141c4d1e62d744912b..ed6da90beac2ef09300ab5472145b52d26bd4cc9 100644
--- a/ui/ozone/platform/drm/host/gpu_thread_observer.h
+++ b/ui/ozone/platform/drm/host/gpu_thread_observer.h
@@ -12,10 +12,15 @@ class GpuThreadObserver {
  public:
   virtual ~GpuThreadObserver() {}
 
+  // Called when the GPU process is launched.
+  // This is called from browser IO thread.
+  virtual void OnGpuProcessLaunched() = 0;
   // Called when a GPU thread implementation has become available.
+  // This is called from browser UI thread.
   virtual void OnGpuThreadReady() = 0;
   // Called when the GPU thread implementation has ceased to be
   // available.
+  // This is called from browser UI thread.
   virtual void OnGpuThreadRetired() = 0;
 };