Reapplies all the IPC system work (reverts the revert r56272).

chrome/browser/importer/firefox_importer_unittest_utils_mac.cc

Index: chrome/browser/importer/firefox_importer_unittest_utils_mac.cc
diff --git a/chrome/browser/importer/firefox_importer_unittest_utils_mac.cc b/chrome/browser/importer/firefox_importer_unittest_utils_mac.cc
index c20940f4558b2e25f421bdf6ae7fd3c95464b5c0..859811e0d48d650a6918dfaf41167f542d8d1814 100644
--- a/chrome/browser/importer/firefox_importer_unittest_utils_mac.cc
+++ b/chrome/browser/importer/firefox_importer_unittest_utils_mac.cc
@@ -16,11 +16,16 @@
 #include "ipc/ipc_switches.h"
 #include "testing/multiprocess_func_list.h"
 
-// Definition of IPC Messages used for this test.
+// Declaration of IPC Messages used for this test.
 #define MESSAGES_INTERNAL_FILE \
     "chrome/browser/importer/firefox_importer_unittest_messages_internal.h"
 #include "ipc/ipc_message_macros.h"
 
+// Definition of IPC Messages used for this test.
+#define MESSAGES_INTERNAL_IMPL_FILE \
+  "chrome/browser/importer/firefox_importer_unittest_messages_internal.h"
+#include "ipc/ipc_message_impl_macros.h"
+
 namespace {
 
 // Name of IPC Channel to use for Server<-> Child Communications.