win: Add version to client registration request

util/win/registration_protocol_win.h

Index: util/win/registration_protocol_win.h
diff --git a/util/win/registration_protocol_win.h b/util/win/registration_protocol_win.h
index dbd6cb5645f8fe73075aeaf754da5051255dbf60..e2f1d23d17abe5d77c3496f5e7a1fb472b90986d 100644
--- a/util/win/registration_protocol_win.h
+++ b/util/win/registration_protocol_win.h
@@ -38,12 +38,20 @@ struct ExceptionInformation {
 
 //! \brief A client registration request.
 struct RegistrationRequest {
-  //! \brief The address, in the client process address space, of an
-  //!     ExceptionInformation structure.
-  WinVMAddress exception_information;
+  //! \brief The expected value of `version`. This should be changed whenever
+  //!     the messages or ExceptionInformation are modified incompatibly.
+  enum { kMessageVersion = 1 };
+
+  //! \brief Version field to detect skew between client and server. Should be
+  //!     set to kMessageVersion.
+  int version;
 
   //! \brief The PID of the client process.
   DWORD client_process_id;

[Mark Mentovai, 2015/09/04 16:05:55]

Nice repacking. :)

[scottmg, 2015/09/04 18:50:00]

Tell me 20 or 30 times and eventually I remember. :)

+
+  //! \brief The address, in the client process address space, of an
+  //!     ExceptionInformation structure.
+  WinVMAddress exception_information;
 };
 
 //! \brief A message only sent to the server by itself to trigger shutdown.