MojoCompositorFrameSinkPrivate should support copy requests

cc/output/copy_output_request.h

 // Copyright 2013 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.
 
 #ifndef CC_OUTPUT_COPY_OUTPUT_REQUEST_H_
 #define CC_OUTPUT_COPY_OUTPUT_REQUEST_H_
 
 #include <memory>
 
 #include "base/callback.h"
@@ skipping 65 matching lines @@
 
   void SendEmptyResult();
   void SendBitmapResult(std::unique_ptr<SkBitmap> bitmap);
   void SendTextureResult(
       const gfx::Size& size,
       const TextureMailbox& texture_mailbox,
       std::unique_ptr<SingleReleaseCallback> release_callback);
 
   void SendResult(std::unique_ptr<CopyOutputResult> result);
 
+  void set_result_callback(CopyOutputRequestCallback result_callback) {

[danakj, 2017/02/06 23:02:12]

This looks like what CreateRelayRequest is for, to make a new CopyOutputRequest
with a new callback?

[Saman Sami, 2017/02/06 23:09:54]

Yeah, you're right. I can fix that, but do we have to make an unnecessary copy?

[danakj, 2017/02/06 23:24:08]

It's not a copy of much, what are you concerned for? And it keeps the internals
private.

[Saman Sami, 2017/02/13 23:07:37]

Pretty much every private member has a setter though?

[danakj, 2017/02/13 23:11:15]

Yes but this the thing that ensures the callback is run, it's passed in the
constructor unlike the other things. If you replace the callback now errors and
what is getting replied to gets much more complicated. I think the relationship
that a CopyOutputRequest is tied to a fixed callback is valuable and this would
allow much more difficult to understand things to happen, even if in this case
it's not bad. I don't want to see these methods added here for those reasons.

[danakj, 2017/02/13 23:12:19]

This along with the fact there is already a way to do this, with a RelayRequest.
This adds new APIs that are not needed.

+    result_callback_ = result_callback;
+  }
+
+  const CopyOutputRequestCallback& result_callback() {
+    return result_callback_;
+  }
+
  private:
   friend struct mojo::StructTraits<mojom::CopyOutputRequestDataView,
                                    std::unique_ptr<CopyOutputRequest>>;
 
   CopyOutputRequest();
   CopyOutputRequest(bool force_bitmap_result,
                     const CopyOutputRequestCallback& result_callback);
 
   base::Optional<base::UnguessableToken> source_;
   bool force_bitmap_result_;
   base::Optional<gfx::Rect> area_;
   base::Optional<TextureMailbox> texture_mailbox_;
   CopyOutputRequestCallback result_callback_;
 
   DISALLOW_COPY_AND_ASSIGN(CopyOutputRequest);
 };
 
 }  // namespace cc
 
 #endif  // CC_OUTPUT_COPY_OUTPUT_REQUEST_H_