[Ozone-DRI] Remove the extra helper thread and reuse the IO one

ui/ozone/platform/dri/dri_gpu_platform_support.h

Index: ui/ozone/platform/dri/dri_gpu_platform_support.h
diff --git a/ui/ozone/platform/dri/dri_gpu_platform_support.h b/ui/ozone/platform/dri/dri_gpu_platform_support.h
index daae2ec731f939c9c6bc43ac724ba9b0d2ecbe14..23257bf7a34c93c5d5a2d5646dc1b3deb2d3af51 100644
--- a/ui/ozone/platform/dri/dri_gpu_platform_support.h
+++ b/ui/ozone/platform/dri/dri_gpu_platform_support.h
@@ -10,13 +10,13 @@
 #include "base/memory/scoped_vector.h"
 #include "ipc/message_filter.h"
 #include "ui/gfx/native_widget_types.h"
-#include "ui/ozone/platform/dri/dri_helper_thread.h"
 #include "ui/ozone/public/gpu_platform_support.h"
 
 class SkBitmap;
 
 namespace base {
 class FilePath;
+class SingleThreadTaskRunner;
 }
 
 namespace gfx {
@@ -77,17 +77,18 @@ class DriGpuPlatformSupport : public GpuPlatformSupport {
   void OnAddGraphicsDevice(const base::FilePath& path);
   void OnRemoveGraphicsDevice(const base::FilePath& path);
 
-  void OnFilterAdded();
+  void SetIOTaskRunner(
+      const scoped_refptr<base::SingleThreadTaskRunner>& io_task_runner);
 
   IPC::Sender* sender_;                       // Not owned.
   DriWrapper* drm_;                           // Not owned.
   DriWindowDelegateManager* window_manager_;  // Not owned.
   ScreenManager* screen_manager_;             // Not owned.
 
-  DriHelperThread helper_thread_;
   scoped_ptr<NativeDisplayDelegateDri> ndd_;
   ScopedVector<GpuPlatformSupport> handlers_;
   scoped_refptr<IPC::MessageFilter> filter_;
+  scoped_refptr<base::SingleThreadTaskRunner> io_task_runner_;
 };
 
 }  // namespace ui