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

chrome/browser/sync/protocol/sync.proto

 // 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.
 //
 // Sync protocol for communication between sync client and server.
 
 // 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 "app_notification_specifics.proto";
+import "app_setting_specifics.proto";
+import "app_specifics.proto";
+import "autofill_specifics.proto";
+import "bookmark_specifics.proto";
+import "extension_setting_specifics.proto";
+import "extension_specifics.proto";
+import "nigori_specifics.proto";
+import "password_specifics.proto";
+import "preference_specifics.proto";
+import "search_engine_specifics.proto";
+import "session_specifics.proto";
+import "theme_specifics.proto";
+import "typed_url_specifics.proto";
 import "encryption.proto";
 import "sync_enums.proto";
 import "client_commands.proto";
 import "client_debug_info.proto";
 
 // Used for inspecting how long we spent performing operations in different
 // backends. All times must be in millis.
 message ProfilingData {
   optional int64 meta_data_write_time = 1;
   optional int64 file_data_write_time = 2;
@@ skipping 26 matching lines @@
   //   - MyDatatypeSpecifics is the type (probably a message type defined
   //     in your new .proto file) that you want to associate with each
   //     object of the new datatype.
   //   - my_datatype is the field identifier you'll use to access the
   //     datatype specifics from the code.
   //
   // Server implementations are obligated to preserve the contents of
   // EntitySpecifics when it contains unrecognized extensions.  In this
   // way, it is possible to add new datatype fields without having
   // to update the server.
-  extensions 30000 to max;
+
+  optional AutofillSpecifics autofill = 31729;
+  optional ExtensionSettingSpecifics extension_setting = 96159;
+  optional ExtensionSpecifics extension = 48119;
+  optional NigoriSpecifics nigori = 47745;
+  optional PasswordSpecifics password = 45873;
+  optional PreferenceSpecifics preference = 37702;
+  optional SearchEngineSpecifics search_engine = 88610;
+  optional SessionSpecifics session = 50119;
+  optional ThemeSpecifics theme = 41210;
+  optional TypedUrlSpecifics typed_url = 40781;
+  optional BookmarkSpecifics bookmark = 32904;
+  optional AppNotification app_notification = 45184;
+  optional AppSettingSpecifics app_setting = 103656;
+  optional AppSpecifics app = 48364;
+  optional AutofillProfileSpecifics autofill_profile = 63951;
 }
 
 message SyncEntity {
   // This item's identifier.  In a commit of a new item, this will be a
   // client-generated ID.  If the commit succeeds, the server will generate
   // a globally unique ID and return it to the committing client in the
   // CommitResponse.EntryResponse.  In the context of a GetUpdatesResponse,
   // |id_string| is always the server generated ID.  The original
   // client-generated ID is preserved in the |originator_client_id| field.
   // Present in both GetUpdatesResponse and CommitMessage.
@@ skipping 563 matching lines @@
   optional string store_birthday = 6;
 
   optional ClientCommand client_command = 7;
   optional ProfilingData profiling_data = 8;
 
   // The data types whose storage has been migrated.  Present when the value of
   // error_code is MIGRATION_DONE.
   repeated int32 migrated_data_type_id = 12;
 };