Implement off-the-wire validation scheme for enum types.

ipc/param_traits_write_macros.h

Index: ipc/param_traits_write_macros.h
diff --git a/ipc/param_traits_write_macros.h b/ipc/param_traits_write_macros.h
index dd977cde8d8ace40a3251025e541f678c4f20a53..81f915ffff8dedf95bb36766f779fc1bc05d93f3 100644
--- a/ipc/param_traits_write_macros.h
+++ b/ipc/param_traits_write_macros.h
@@ -9,13 +9,11 @@
 #include "ipc/ipc_message_null_macros.h"
 
 // STRUCT declarations cause corresponding STRUCT_TRAITS declarations to occur.
-#undef IPC_STRUCT_BEGIN
 #undef IPC_STRUCT_BEGIN_WITH_PARENT
 #undef IPC_STRUCT_MEMBER
 #undef IPC_STRUCT_END
 #define IPC_STRUCT_BEGIN_WITH_PARENT(struct_name, parent) \
-  IPC_STRUCT_BEGIN(struct_name)
-#define IPC_STRUCT_BEGIN(struct_name) IPC_STRUCT_TRAITS_BEGIN(struct_name)
+  IPC_STRUCT_TRAITS_BEGIN(struct_name)
 #define IPC_STRUCT_MEMBER(type, name, ...) IPC_STRUCT_TRAITS_MEMBER(name)
 #define IPC_STRUCT_END() IPC_STRUCT_TRAITS_END()
 
@@ -30,10 +28,11 @@
 #define IPC_STRUCT_TRAITS_PARENT(type) ParamTraits<type>::Write(m, p);
 #define IPC_STRUCT_TRAITS_END() }
 
-#undef IPC_ENUM_TRAITS
-#define IPC_ENUM_TRAITS(enum_name) \
-  void ParamTraits<enum_name>::Write(Message* m, const param_type& p) { \
-    m->WriteInt(static_cast<int>(p)); \
+#undef IPC_ENUM_TRAITS_VALIDATE
+#define IPC_ENUM_TRAITS_VALIDATE(enum_name, validation_expression) \
+  void ParamTraits<enum_name>::Write(Message* m, const param_type& value) { \
+    DCHECK(validation_expression); \
+    m->WriteInt(static_cast<int>(value)); \
   }
 
 #endif  // IPC_PARAM_TRAITS_WRITE_MACROS_H_