mem: add extension mechanism into Request

Change-Id: Ie144e0cf243bab6d9ddbea79caf559c7e774a787
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/67958
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Yu-hsin Wang <yuhsingw@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>

src/mem/request.hh

@@ -58,6 +58,7 @@
 
 #include "base/amo.hh"
 #include "base/compiler.hh"
+#include "base/extensible.hh"
 #include "base/flags.hh"
 #include "base/types.hh"
 #include "cpu/inst_seq.hh"
@@ -93,7 +94,7 @@ class ThreadContext;
 typedef std::shared_ptr<Request> RequestPtr;
 typedef uint16_t RequestorID;
 
-class Request
+class Request : public Extensible<Request>
 {
   public:
     typedef uint64_t FlagsType;
@@ -501,7 +502,8 @@ class Request
     }
 
     Request(const Request& other)
-        : _paddr(other._paddr), _size(other._size),
+        : Extensible<Request>(other),
+          _paddr(other._paddr), _size(other._size),
           _byteEnable(other._byteEnable),
           _requestorId(other._requestorId),
           _flags(other._flags),