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

chrome/browser/sync/protocol/app_specifics.proto

 // Copyright (c) 2011 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.
 //
 // Sync protocol datatype extension for apps.
 
 // Update proto_value_conversions{.h,.cc,_unittest.cc} if you change
 // any fields in this file.
 
 syntax = "proto2";
 
 option optimize_for = LITE_RUNTIME;
 option retain_unknown_fields = true;
 
 package sync_pb;
 
-import "sync.proto";
 import "extension_specifics.proto";
 
 // Settings related to push notifications for apps.
 message AppNotificationSettings {
   // DEPRECATED: Use oauth_client_id below.
   // Whether or not the user has setup notifications at least once.
   // The value for this field will start out false and will be set
   // to true when the user accepts receiving notifications for the
   // first time and then it will always remain true.
   optional bool initial_setup_done = 1;
@@ skipping 24 matching lines @@
 
   // This controls where on a page this application icon will appear.
   optional string app_launch_ordinal = 3;
 
   // This specifics which page the application icon will appear on in the NTP.
   // This values only provide the order within the application pages, not within
   // all of the panels in the NTP.
   optional string page_ordinal = 4;
 }
 
-extend EntitySpecifics {
-  optional AppSpecifics app = 48364;
-}