Expedite discovery of primary DRM device.

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

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_OZONE_PLATFORM_DRM_HOST_GPU_THREAD_OBSERVER_H_
 #define UI_OZONE_PLATFORM_DRM_HOST_GPU_THREAD_OBSERVER_H_
 
 namespace ui {
 
 // Observes the channel state.
 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;
 };
 
 }  // namespace ui
 
 #endif  // UI_OZONE_PLATFORM_DRM_HOST_GPU_THREAD_OBSERVER_H_