Introducing gpu::CommandBufferId as a distinct, IdType<...>-based type.

content/browser/download/save_types.h

 // Copyright (c) 2012 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 CONTENT_BROWSER_DOWNLOAD_SAVE_TYPES_H_
 #define CONTENT_BROWSER_DOWNLOAD_SAVE_TYPES_H_
 
 #include <stdint.h>
 
 #include <map>
 #include <string>
 #include <utility>
 #include <vector>
 
 #include "base/files/file_path.h"
-#include "content/common/id_type.h"
+#include "gpu/command_buffer/common/id_type.h"
 #include "url/gurl.h"
 
 namespace content {
 
 class SavePackage;
-using SavePackageId = IdType32<SavePackage>;
+using SavePackageId = gpu::IdType32<SavePackage>;

[piman, 2016/02/09 23:29:32]

Yeah, this is technically permitted, but really really odd.

[Łukasz Anforowicz, 2016/02/10 22:18:14]

Let me add nick@ to the reviewer's line.  Nick - WDYT?

[ncarter (slow), 2016/02/10 23:34:16]

I think it should go in base/, but if we can't put it there, I guess we can live
with this.

The other approach is to leave content/common/id_type intact and hide the ugly
import of gpu from there?

[Łukasz Anforowicz, 2016/02/11 16:51:25]

Ok.
Right - we could include gpu/.../id_type.h from content/common/id_type.h and
have 5 type aliases from |content| namespace into |gpu| namespace like:

  namespace content {

  template<T1,T2,T3>
  using IdType<T1,T2,T3> = gpu::IdType<T1,T2,T3>;

  template<T>
  using IdType32<T> = gpu::IdType32<T>;

I think I prefer the lesser evil of what we currently have in the CL, because

1. The proposed type aliases would only help users of IdType under //content
(i.e. the type aliases don't help with adopting IdType elsewhere).

2. The extra file makes IdType approach look messier IMO (i.e. it makes IdType
"implementation" spread across even more files).

 
 class SaveItem;
-using SaveItemId = IdType32<SaveItem>;
+using SaveItemId = gpu::IdType32<SaveItem>;
 
 // Map from save_item_id into final file path.
 using FinalNamesMap = std::map<SaveItemId, base::FilePath>;
 
 // This structure is used to handle and deliver some info
 // when processing each save item job.
 struct SaveFileCreateInfo {
   enum SaveFileSource {
     // This type indicates the source is not set.
     SAVE_FILE_FROM_UNKNOWN = -1,
@@ skipping 49 matching lines @@
   std::string content_disposition;
   // Total bytes of saved file.
   int64_t total_bytes;
   // Source type of saved file.
   SaveFileSource save_source;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_DOWNLOAD_SAVE_TYPES_H_