viz: Use a simple GpuMemoryBufferManager implementation.

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 0cf5d3c985e15ad954d1a545bd2abadb77235811..21b6c24e90840e2c125c31b819731dcadad5ef77 100644
--- a/services/ui/gpu/gpu_service.h
+++ b/services/ui/gpu/gpu_service.h
@@ -73,6 +73,9 @@ class GpuService : public gpu::GpuChannelManagerDelegate,
   }
 
   gpu::ImageFactory* gpu_image_factory();
+  gpu::GpuMemoryBufferFactory* gpu_memory_buffer_factory() {
+    return gpu_memory_buffer_factory_.get();
+  }
 
   gpu::GpuWatchdogThread* watchdog_thread() { return watchdog_thread_.get(); }