mus-gpu: Bind GpuMain on the gpu thread.

services/ui/gpu/gpu_service.h

Index: services/ui/gpu/gpu_service.h
diff --git a/services/ui/gpu/gpu_service.h b/services/ui/gpu/gpu_service.h
index f07519bb66312c6f3bc65ba66714bbaeb9f84506..d6e2d3f583a1e7e3bb4990f9f2f6837c99b5beff 100644
--- a/services/ui/gpu/gpu_service.h
+++ b/services/ui/gpu/gpu_service.h
@@ -61,6 +61,8 @@ class GpuService : public gpu::GpuChannelManagerDelegate,
                           base::WaitableEvent* shutdown_event = nullptr);
   void Bind(mojom::GpuServiceRequest request);
 
+  bool is_initialized() const { return !!gpu_host_; }
+
   media::MediaGpuChannelManager* media_gpu_channel_manager() {
     return media_gpu_channel_manager_.get();
   }