FBTF: Allow forward declaration of classes passed to sync IPC messages.

ipc/ipc_sync_channel_unittest.cc

Index: ipc/ipc_sync_channel_unittest.cc
diff --git a/ipc/ipc_sync_channel_unittest.cc b/ipc/ipc_sync_channel_unittest.cc
index 87e977330fcda887cc981c23a126b0a795cc5a12..a3b757a14f82f6e3ec63c2632f81c9c0ca64476a 100644
--- a/ipc/ipc_sync_channel_unittest.cc
+++ b/ipc/ipc_sync_channel_unittest.cc
@@ -26,6 +26,10 @@
 #define MESSAGES_INTERNAL_FILE "ipc/ipc_sync_message_unittest.h"
 #include "ipc/ipc_message_macros.h"
 
+// Definition of IPC Messages used for this test.
+#define MESSAGES_INTERNAL_IMPL_FILE "ipc/ipc_sync_message_unittest.h"
+#include "ipc/ipc_message_impl_macros.h"
+
 using namespace IPC;
 using base::WaitableEvent;