Change behaivor to decide whether a search engine should be shown in the default list

components/sync/protocol/search_engine_specifics.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 datatype extension for custom search engines.
 
 // Update proto_value_conversions{.h,.cc,_unittest.cc} if you change
 // any fields in this file.
 
 syntax = "proto2";
@@ skipping 15 matching lines @@
   // A flag signifying whether it is safe to automatically modify this search
   // engine entry or not.
   optional bool safe_for_autoreplace = 5;
   // The URL to the OSD file this search engine entry came from.
   optional string originating_url = 6;
   // The date this search engine entry was created. A UTC timestamp with units
   // in microseconds.
   optional int64 date_created = 7;
   // A list of supported input encodings.
   optional string input_encodings = 8;
-  // Whether this entry is shown in the list of default search engines or not.
-  optional bool show_in_default_list = 9;
+  // Obsolete field. This used to represent whether or not this entry is shown
+  // in the list of default search engines.
+  // optional bool deprecated_show_in_default_list = 9;
   // The parameterized URL that provides suggestions as the user types.
   optional string suggestions_url = 10;
   // The ID associated with the prepopulate data this search engine comes from.
   // Set to zero if it was not prepopulated.
   optional int32 prepopulate_id = 11;
   // DEPRECATED: Whether to autogenerate a keyword for the search engine or not.
   // Do not write to this field in the future.  We preserve this for now so we
   // can read the field in order to migrate existing data that sets this bit.
   optional bool autogenerate_keyword = 12;
   // ID 13 reserved - previously used by |logo_id|, now deprecated.
@@ skipping 23 matching lines @@
   // The following post_params are comma-separated lists used to specify the
   // post parameters for the corresponding search URL.
   optional string search_url_post_params = 22;
   optional string suggestions_url_post_params = 23;
   optional string instant_url_post_params = 24;
   optional string image_url_post_params = 25;
 
   // The parameterized URL for a search provider specified new tab page.
   optional string new_tab_url = 26;
 }