services/ui: Allow injecting the IO thread task runner for gpu channel.

services/ui/public/cpp/gpu_service.h

Index: services/ui/public/cpp/gpu_service.h
diff --git a/services/ui/public/cpp/gpu_service.h b/services/ui/public/cpp/gpu_service.h
index a1155ae0bdc3745714270da2455db5d2c75720fc..f6d0104fd0df8afd639204e2e33393b246d93a0b 100644
--- a/services/ui/public/cpp/gpu_service.h
+++ b/services/ui/public/cpp/gpu_service.h
@@ -35,8 +35,13 @@ class GpuService : public gpu::GpuChannelHostFactory,
   }
 
   // The GpuService has to be initialized in the main thread before establishing
-  // the gpu channel.
-  static std::unique_ptr<GpuService> Initialize(shell::Connector* connector);
+  // the gpu channel. The IO thread task-runner needed for the gpu channel can
+  // be set using SetIOTaskRunner(). If no task-runner is set, then a new thread
+  // is created for IO instead.
+  static std::unique_ptr<GpuService> Create(shell::Connector* connector);
+
+  void SetIOThreadTaskRunner(
+      scoped_refptr<base::SingleThreadTaskRunner> task_runner);
 
   // gpu::GpuChannelEstablishFactory:
   void EstablishGpuChannel(
@@ -65,9 +70,10 @@ class GpuService : public gpu::GpuChannelHostFactory,
       size_t size) override;
 
   scoped_refptr<base::SingleThreadTaskRunner> main_task_runner_;
+  scoped_refptr<base::SingleThreadTaskRunner> io_task_runner_;
   shell::Connector* connector_;
   base::WaitableEvent shutdown_event_;
-  base::Thread io_thread_;
+  std::unique_ptr<base::Thread> io_thread_;
   std::unique_ptr<MojoGpuMemoryBufferManager> gpu_memory_buffer_manager_;
 
   // Lock for |gpu_channel_|, |establish_callbacks_| & |is_establishing_|.