Update //third_party/protobuf to version 3.

sync/internal_api/write_node.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "sync/internal_api/public/write_node.h"
 
 #include <stdint.h>
 
 #include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
@@ skipping 145 matching lines @@
   CHECK(!new_value.password().has_client_only_encrypted_data());
   DCHECK_NE(new_specifics_type, UNSPECIFIED);
   DVLOG(1) << "Writing entity specifics of type "
            << ModelTypeToString(new_specifics_type);
   DCHECK_EQ(new_specifics_type, GetModelType());
 
   // Preserve unknown fields.
   const sync_pb::EntitySpecifics& old_specifics = entry_->GetSpecifics();
   sync_pb::EntitySpecifics new_specifics;
   new_specifics.CopyFrom(new_value);
-  new_specifics.mutable_unknown_fields()->MergeFrom(
-      old_specifics.unknown_fields());
+  new_specifics.mutable_unknown_fields()
+      ->append(old_specifics.unknown_fields());
 
   // Will update the entry if encryption was necessary.
   if (!UpdateEntryWithEncryption(GetTransaction()->GetWrappedTrans(),
                                  new_specifics,
                                  entry_)) {
     return;
   }
   if (entry_->GetSpecifics().has_encrypted()) {
     // EncryptIfNecessary already updated the entry for us and marked for
     // syncing if it was needed. Now we just make a copy of the unencrypted
@@ skipping 289 matching lines @@
   syncable::Id predecessor_id =
       predecessor ? predecessor->GetSyncId() : syncable::Id();
   return entry_->PutPredecessor(predecessor_id);
 }
 
 void WriteNode::MarkForSyncing() {
   syncable::MarkForSyncing(entry_);
 }
 
 }  // namespace syncer