[Android] Allow setting recently visited search engines as default search engine

components/search_engines/template_url_service.cc

 // Copyright 2014 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 "components/search_engines/template_url_service.h"
 
 #include <algorithm>
 #include <utility>
 
 #include "base/auto_reset.h"
@@ skipping 1624 matching lines @@
   if (!urls)
     return true;
   for (TemplateURLSet::const_iterator i(urls->begin()); i != urls->end(); ++i) {
     if (!(*i)->safe_for_autoreplace())
       return false;
   }
   return true;
 }
 
 bool TemplateURLService::CanReplace(const TemplateURL* t_url) {
-  return (t_url != default_search_provider_ && !t_url->show_in_default_list() &&
-          t_url->safe_for_autoreplace());
+  return (t_url != default_search_provider_ && t_url->prepopulate_id() <= 0 &&
+          !t_url->created_by_policy() && t_url->safe_for_autoreplace());
 }
 
 TemplateURL* TemplateURLService::FindNonExtensionTemplateURLForKeyword(
     const base::string16& keyword) {
   TemplateURL* keyword_turl = GetTemplateURLForKeyword(keyword);
   if (!keyword_turl || (keyword_turl->type() == TemplateURL::NORMAL))
     return keyword_turl;
   // The extension keyword in the model may be hiding a replaceable
   // non-extension keyword.  Look for it.
   for (const auto& turl : template_urls_) {
@@ skipping 450 matching lines @@
     data.favicon_url = GURL();
   }
   data.safe_for_autoreplace = false;
   data.last_modified = clock_->Now();
   return UpdateNoNotify(url, TemplateURL(data));
 }
 
 void TemplateURLService::NotifyObservers() {
   if (!loaded_)
     return;
-
   FOR_EACH_OBSERVER(TemplateURLServiceObserver, model_observers_,
                     OnTemplateURLServiceChanged());
 }
 
 // |template_urls| are the TemplateURLs loaded from the database.
 // |default_from_prefs| is the default search provider from the preferences, or
 // NULL if the DSE is not policy-defined.
 //
 // This function removes from the vector and the database all the TemplateURLs
 // that were set by policy, unless it is the current default search provider, in
@@ skipping 346 matching lines @@
 
   if (most_recently_intalled_default) {
     base::AutoReset<DefaultSearchChangeOrigin> change_origin(
         &dsp_change_origin_, DSP_CHANGE_OVERRIDE_SETTINGS_EXTENSION);
     default_search_manager_.SetExtensionControlledDefaultSearchEngine(
         most_recently_intalled_default->data());
   } else {
     default_search_manager_.ClearExtensionControlledDefaultSearchEngine();
   }
 }