GpuMain: Fix thread_runner() access DCHECK fail

services/ui/gpu/gpu_main.h

Index: services/ui/gpu/gpu_main.h
diff --git a/services/ui/gpu/gpu_main.h b/services/ui/gpu/gpu_main.h
index a5c859d94601174f2d31c91c181bc87cca29847c..fb9adb49ec31d09e813afaec49143ce1a4309ad0 100644
--- a/services/ui/gpu/gpu_main.h
+++ b/services/ui/gpu/gpu_main.h
@@ -86,6 +86,7 @@ class GpuMain : public gpu::GpuSandboxHelper, public mojom::GpuMain {
 
   // 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_;
@@ -96,6 +97,7 @@ class GpuMain : public gpu::GpuSandboxHelper, public mojom::GpuMain {
   // 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_;