[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 377 matching lines @@
   // We don't have a TemplateURL with keyword.  We still may not allow this
   // keyword if there's evidence we may have created this keyword before and
   // the user renamed it (because, for instance, the keyword is a common word
   // that may interfere with search queries).  An easy heuristic for this is
   // whether the user has a TemplateURL that has been manually modified (e.g.,
   // renamed) connected to the same host.
   return !url.is_valid() || url.host().empty() ||
       CanAddAutogeneratedKeywordForHost(url.host());
 }
 
+bool TemplateURLService::ShowInPrepopulatedList(const TemplateURL* t_url) {
+  return (t_url->prepopulate_id() > 0 || t_url->created_by_policy()) &&
+      t_url->SupportsReplacement(search_terms_data());
+}
+
 bool TemplateURLService::ShowInDefaultList(const TemplateURL* t_url) {
-  return (t_url == default_search_provider_ || t_url->prepopulate_id() > 0 ||
-          t_url->created_by_policy()) &&
-         t_url->SupportsReplacement(search_terms_data());
+  return (t_url == default_search_provider_  &&
+      t_url->SupportsReplacement(search_terms_data())) ||

[Peter Kasting, 2016/11/23 21:30:27]

I don't think we should explicitly check SupportsReplacement() here, since if
something is already the default search provider, it presumably supports
replacement, but even if somehow it doesn't, it surely should be shown in the
default list.

[ltian, 2016/11/29 02:44:03]

Done.

+      ShowInPrepopulatedList(t_url);
 }
 
 void TemplateURLService::AddMatchingKeywords(
     const base::string16& prefix,
     bool supports_replacement_only,
     TURLsAndMeaningfulLengths* matches) {
   AddMatchingKeywordsHelper(
       keyword_to_turl_and_length_, prefix, supports_replacement_only, matches);
 }
 
@@ skipping 2063 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();
   }
 }