add IPC_MESSAGE_EXPORT to IPC_STRUCT_BEGIN.

ipc/ipc_message_macros.h

Index: ipc/ipc_message_macros.h
diff --git a/ipc/ipc_message_macros.h b/ipc/ipc_message_macros.h
index 63faa486147f17cb4cc99fb0df5b27b997ee849c..77a841547fbf721f2a5b9b2c90d0f3c0b9613487 100644
--- a/ipc/ipc_message_macros.h
+++ b/ipc/ipc_message_macros.h
@@ -183,22 +183,22 @@
 #include "ipc/ipc_message_utils_impl.h"
 #endif
 
+// Override this to force message classes to be exported.
+#ifndef IPC_MESSAGE_EXPORT
+#define IPC_MESSAGE_EXPORT
+#endif
+
 // Macros for defining structs.  May be subsequently redefined.
 #define IPC_STRUCT_BEGIN(struct_name) \
   struct struct_name; \
   IPC_STRUCT_TRAITS_BEGIN(struct_name) \
   IPC_STRUCT_TRAITS_END() \
-  struct struct_name : IPC::NoParams { \
+  struct IPC_MESSAGE_EXPORT struct_name : IPC::NoParams { \
     struct_name(); \
     ~struct_name();
 #define IPC_STRUCT_MEMBER(type, name) type name;
 #define IPC_STRUCT_END() };
 
-// Override this to force message classes to be exported.
-#ifndef IPC_MESSAGE_EXPORT
-#define IPC_MESSAGE_EXPORT
-#endif
-
 // Message macros collect specific numbers of arguments and funnel them into
 // the common message generation macro.  These should never be redefined.
 #define IPC_MESSAGE_CONTROL0(msg_class) \