mus-gpu: Include GpuPreferences when requesting for GpuService.

services/ui/gpu/interfaces/gpu_host.mojom

 // 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.
 
 module ui.mojom;
 
 import "gpu/ipc/common/gpu_info.mojom";
 import "gpu/ipc/common/surface_handle.mojom";
 import "services/ui/gpu/interfaces/context_lost_reason.mojom";
 import "url/mojo/url.mojom";
 
+// Communication channel from the gpu process to the gpu host. This interface
+// should never have any sync function calls.
 interface GpuHost {
   DidInitialize(gpu.mojom.GpuInfo gpu_info);
   DidCreateOffscreenContext(url.mojom.Url url);
   DidDestroyOffscreenContext(url.mojom.Url url);
 
   DidDestroyChannel(int32 client_id);
   DidLoseContext(bool offscreen,
                  ContextLostReason reason,
                  url.mojom.Url active_url);
 
   SetChildSurface(gpu.mojom.SurfaceHandle parent,
                   gpu.mojom.SurfaceHandle child);
   StoreShaderToDisk(int32 client_id, string key, string shader);
 };