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

ipc/ipc_message_utils.h

Index: ipc/ipc_message_utils.h
diff --git a/ipc/ipc_message_utils.h b/ipc/ipc_message_utils.h
index d8b660740d8b67d1c739efe44be20c950a1f153b..4adeabe630483b1220ca8f4f7d1248a69796555e 100644
--- a/ipc/ipc_message_utils.h
+++ b/ipc/ipc_message_utils.h
@@ -19,6 +19,7 @@
 #include "base/containers/stack_container.h"
 #include "base/files/file.h"
 #include "base/format_macros.h"
+#include "base/id_type.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/scoped_vector.h"
 #include "base/strings/string16.h"
@@ -976,6 +977,27 @@ struct ParamTraits<scoped_ptr<P> > {
   }
 };
 
+template <typename TypeMarker, typename WrappedType, WrappedType kInvalidValue>
+struct ParamTraits<base::IdType<TypeMarker, WrappedType, kInvalidValue>> {
+  typedef base::IdType<TypeMarker, WrappedType, kInvalidValue> param_type;
+  typedef ParamTraits<WrappedType> base_param_traits;
+  static void Write(base::Pickle* m, const param_type& p) {
+    base_param_traits::Write(m, p.GetUnsafeValue());
+  }
+  static bool Read(const base::Pickle* m,
+                   base::PickleIterator* iter,
+                   param_type* r) {
+    WrappedType value;
+    if (!base_param_traits::Read(m, iter, &value))
+      return false;
+    *r = param_type::FromUnsafeValue(value);
+    return true;
+  }
+  static void Log(const param_type& p, std::string* l) {
+    base_param_traits::Log(p.GetUnsafeValue(), l);
+  }
+};

[Nico, 2016/02/09 20:04:29]

This isn't more type-safe than just sending the inner int type, right? Why is it
necessary to send IdTypes over ipc?

[Łukasz Anforowicz, 2016/02/09 23:06:32]

It *is* more type-safe to use gpu::CommandBufferId instead of a raw integer in a
definition of an IPC message (i.e. PpapiHostMsg_PPBGraphics3D_Create in
crrev.com/1548443002/patch/40001/50064).  This means that the constructor of the
message is type-safe (i.e. won't accept a random integer) as are the handlers of
the message (i.e. PPB_Graphics3D_Proxy::OnMsgCreate in
crrev.com/1548443002/patch/40001/50065).  In other words - having IPC support
avoids unnecessary GetUnsafeValue / FromUnsafeValue calls.

+
 // IPC types ParamTraits -------------------------------------------------------
 
 // A ChannelHandle is basically a platform-inspecific wrapper around the