Reusing base::IdType<...> to implement SurfaceId.

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 97b95e986a9237ee881594416e93ebefbf99b875..567e89d9f7a0400718d01fc73f0d4bb3cc55fd06 100644
--- a/ipc/ipc_message_utils.h
+++ b/ipc/ipc_message_utils.h
@@ -17,6 +17,7 @@
 #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"
@@ -858,6 +859,31 @@ struct ParamTraits<scoped_ptr<P> > {
   }
 };
 
+template <typename TypeBeingIdentified,
+          typename WrappedType,
+          WrappedType kInvalidValue>
+struct ParamTraits<
+    base::IdType<TypeBeingIdentified, WrappedType, kInvalidValue>> {
+  typedef base::IdType<TypeBeingIdentified, WrappedType, kInvalidValue>
+      param_type;
+  typedef ParamTraits<WrappedType> base_param_traits;
+  static void Write(Message* m, const param_type& p) {
+    base_param_traits::Write(m, p.GetUnsafeValue());
+  }
+  static bool Read(const Message* 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);
+  }
+};
+
 // IPC types ParamTraits -------------------------------------------------------
 
 // A ChannelHandle is basically a platform-inspecific wrapper around the