CopyOutputRequest must have a working result_callback_ when received over mojo

cc/ipc/copy_output_request.mojom

 // Copyright 2017 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 cc.mojom;
 
+import "cc/ipc/copy_output_result.mojom";
 import "cc/ipc/texture_mailbox.mojom";
 import "mojo/common/unguessable_token.mojom";
 import "ui/gfx/geometry/mojo/geometry.mojom";
 
 // See cc/output/copy_output_request.h.
-// Note: result_callback_ is not included in this struct.
 struct CopyOutputRequest {
   mojo.common.mojom.UnguessableToken? source;
   bool force_bitmap_result;
   gfx.mojom.Rect? area;
-  cc.mojom.TextureMailbox? texture_mailbox;
+  TextureMailbox? texture_mailbox;
+  CopyOutputResultSender result_sender;
 };
+
+// When the display compositor is ready to respond to the CopyOutputRequest,
+// it uses this interface to send back the result.
+interface CopyOutputResultSender {
+  SendResult(CopyOutputResult result);
+};