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

content/browser/download/save_types.h

Index: content/browser/download/save_types.h
diff --git a/content/browser/download/save_types.h b/content/browser/download/save_types.h
index 83d890b8dc9e0ddd3964005af048c254e88a800e..a9ab45c325bc0d5f273245ab85cd48943103e244 100644
--- a/content/browser/download/save_types.h
+++ b/content/browser/download/save_types.h
@@ -13,16 +13,16 @@
 #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>;