GpuMain: Fix thread_runner() access DCHECK fail

services/ui/gpu/gpu_main.h

 // Copyright 2016 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 SERVICES_UI_GPU_GPU_MAIN_H_
 #define SERVICES_UI_GPU_GPU_MAIN_H_
 
 #include "base/threading/thread.h"
 #include "gpu/ipc/in_process_command_buffer.h"
 #include "gpu/ipc/service/gpu_init.h"
@@ skipping 68 matching lines @@
   cc::mojom::DisplayCompositorRequest pending_display_compositor_request_;
   cc::mojom::DisplayCompositorClientPtrInfo
       pending_display_compositor_client_info_;
 
   std::unique_ptr<DisplayCompositor> display_compositor_;
 
   std::unique_ptr<gpu::GpuMemoryBufferFactory> gpu_memory_buffer_factory_;
 
   // The main thread for Gpu.
   base::Thread gpu_thread_;
+  scoped_refptr<base::SingleThreadTaskRunner> gpu_thread_task_runner_;
 
   // The thread that handles IO events for Gpu.
   base::Thread io_thread_;
 
   // The display compositor gets its own thread in mus-gpu. The gpu service,
   // where GL commands are processed resides on its own thread. Various
   // components of the display compositor such as Display, ResourceProvider,
   // and GLRenderer block on sync tokens from other command buffers. Thus,
   // the gpu service must live on a separate thread.
   base::Thread compositor_thread_;
+  scoped_refptr<base::SingleThreadTaskRunner> compositor_thread_task_runner_;
 
   mojo::Binding<mojom::GpuMain> binding_;
 
   DISALLOW_COPY_AND_ASSIGN(GpuMain);
 };
 
 }  // namespace ui
 
 #endif  // SERVICES_UI_GPU_GPU_MAIN_H_