mus/gpu: Introduce the GpuServiceHost mojom interface.

services/ui/gpu/interfaces/gpu_service_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 "services/ui/gpu/interfaces/context_lost_reason.mojom";
+import "url/mojo/url.mojom";
+
+interface GpuServiceHost {
+  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);
+
+  StoreShaderToDisk(int32 client_id, string key, string shader);
+};