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

chrome/browser/webdata/autocomplete_syncable_service.cc

Index: chrome/browser/webdata/autocomplete_syncable_service.cc
diff --git a/chrome/browser/webdata/autocomplete_syncable_service.cc b/chrome/browser/webdata/autocomplete_syncable_service.cc
index b2b2ce795bc8c8b5c13de4ea38d8b9e42ec2441e..d36f7e37854c947d04bfb6622e9acc3368ea29ec 100644
--- a/chrome/browser/webdata/autocomplete_syncable_service.cc
+++ b/chrome/browser/webdata/autocomplete_syncable_service.cc
@@ -10,6 +10,7 @@
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/sync/api/sync_error.h"
 #include "chrome/browser/sync/protocol/autofill_specifics.pb.h"
+#include "chrome/browser/sync/protocol/sync.pb.h"
 #include "chrome/browser/webdata/autofill_table.h"
 #include "chrome/browser/webdata/web_data_service.h"
 #include "chrome/browser/webdata/web_database.h"
@@ -193,10 +194,10 @@ SyncError AutocompleteSyncableService::ProcessSyncChanges(
         CreateOrUpdateEntry(i->sync_data(), db_entries.get(), &new_entries);
         break;
       case SyncChange::ACTION_DELETE: {
-        DCHECK(i->sync_data().GetSpecifics().HasExtension(sync_pb::autofill))
+        DCHECK(i->sync_data().GetSpecifics().has_autofill())
             << "Autofill specifics data not present on delete!";
         const sync_pb::AutofillSpecifics& autofill =
-            i->sync_data().GetSpecifics().GetExtension(sync_pb::autofill);
+            i->sync_data().GetSpecifics().autofill();
         if (autofill.has_value()) {
           list_processing_error = AutofillEntryDelete(autofill);
         } else {
@@ -265,7 +266,7 @@ void AutocompleteSyncableService::CreateOrUpdateEntry(
     std::vector<AutofillEntry>* new_entries) {
   const sync_pb::EntitySpecifics& specifics = data.GetSpecifics();
   const sync_pb::AutofillSpecifics& autofill_specifics(
-      specifics.GetExtension(sync_pb::autofill));
+      specifics.autofill());
 
   if (!autofill_specifics.has_value()) {
     DLOG(WARNING)
@@ -308,7 +309,7 @@ void AutocompleteSyncableService::CreateOrUpdateEntry(
 void AutocompleteSyncableService::WriteAutofillEntry(
     const AutofillEntry& entry, sync_pb::EntitySpecifics* autofill_specifics) {
   sync_pb::AutofillSpecifics* autofill =
-      autofill_specifics->MutableExtension(sync_pb::autofill);
+      autofill_specifics->mutable_autofill();
   autofill->set_name(UTF16ToUTF8(entry.key().name()));
   autofill->set_value(UTF16ToUTF8(entry.key().value()));
   const std::vector<base::Time>& ts(entry.timestamps());