Adds a TransportDIB::Id value that is explicitly invalid and use it when compositing

content/common/common_param_traits.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This file is used to define IPC::ParamTraits<> specializations for a number
 // of types so that they can be serialized over IPC.  IPC::ParamTraits<>
 // specializations for basic types (like int and std::string) and types in the
 // 'base' project can be found in ipc/ipc_message_utils.h.  This file contains
 // specializations for types that are used by the content code, and which need
 // manual serialization code.  This is usually because they're not structs with
@@ skipping 365 matching lines @@
   static void Log(const param_type& p, std::string* l) {
     l->append("TransportDIB(");
     LogParam(p.handle, l);
     l->append(", ");
     LogParam(p.sequence_num, l);
     l->append(")");
   }
 };
 #endif
 
+#if defined(USE_X11)
+template<>
+struct ParamTraits<TransportDIB::Id> {
+  typedef TransportDIB::Id param_type;
+  static void Write(Message* m, const param_type& p) {
+    WriteParam(m, p.shmkey);
+  }
+  static bool Read(const Message* m, void** iter, param_type* r) {
+    return (ReadParam(m, iter, &r->shmkey));

[brettw, 2011/03/24 23:54:34]

I wouldn't do the extra parens around ReadParam.

+  }
+  static void Log(const param_type& p, std::string* l) {
+    l->append("TransportDIB(");
+    LogParam(p.shmkey, l);
+    l->append(")");
+  }
+};
+#endif
+
 template <>
 struct SimilarTypeTraits<WebKit::WebTextDirection> {
   typedef int Type;
 };
 
 template <>
 struct ParamTraits<SkBitmap> {
   typedef SkBitmap param_type;
   static void Write(Message* m, const param_type& p);
 
@@ skipping 13 matching lines @@
 struct ParamTraits<webkit_glue::PasswordForm> {
   typedef webkit_glue::PasswordForm param_type;
   static void Write(Message* m, const param_type& p);
   static bool Read(const Message* m, void** iter, param_type* p);
   static void Log(const param_type& p, std::string* l);
 };
 
 }  // namespace IPC
 
 #endif  // CONTENT_COMMON_COMMON_PARAM_TRAITS_H_