sync: remove use of protobuf extensions in protocol to reduce static init overhead.

chrome/browser/sync/internal_api/change_record_unittest.cc

Index: chrome/browser/sync/internal_api/change_record_unittest.cc
diff --git a/chrome/browser/sync/internal_api/change_record_unittest.cc b/chrome/browser/sync/internal_api/change_record_unittest.cc
index e9cb3a4f69fea02ba6192e58084adc32554587eb..edb2ae14812446a1e13463a7f0148eb1bb49f63e 100644
--- a/chrome/browser/sync/internal_api/change_record_unittest.cc
+++ b/chrome/browser/sync/internal_api/change_record_unittest.cc
@@ -75,9 +75,9 @@ class MockExtraChangeRecordData
 
 TEST_F(ChangeRecordTest, ChangeRecordToValue) {
   sync_pb::EntitySpecifics old_specifics;
-  old_specifics.MutableExtension(sync_pb::extension)->set_id("old");
+  old_specifics.mutable_extension()->set_id("old");
   sync_pb::EntitySpecifics new_specifics;
-  old_specifics.MutableExtension(sync_pb::extension)->set_id("new");
+  old_specifics.mutable_extension()->set_id("new");
 
   const int64 kTestId = 5;