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

components/search_engines/template_url_service.h

 // 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.
 
 #ifndef COMPONENTS_SEARCH_ENGINES_TEMPLATE_URL_SERVICE_H_
 #define COMPONENTS_SEARCH_ENGINES_TEMPLATE_URL_SERVICE_H_
 
 #include <stddef.h>
 
 #include <list>
@@ skipping 115 matching lines @@
   // keyword/url pair, or there is one but it can be replaced. If there is an
   // existing keyword that can be replaced and template_url_to_replace is
   // non-NULL, template_url_to_replace is set to the keyword to replace.
   //
   // |url| is the URL of the search query.  This is used to prevent auto-adding
   // a keyword for hosts already associated with a manually-edited keyword.
   bool CanAddAutogeneratedKeyword(const base::string16& keyword,
                                   const GURL& url,
                                   TemplateURL** template_url_to_replace);
 
+  // Retruns whether |template_url| should be shown in the list of engines
+  // prepopulated by Chrome browser.

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

Nit: Typo + grammar

Because you are splitting the existing functionality of ShowInDefaultList() into
pieces, you should aim to split its comment into pieces as well.  All that stuff
about "most likely choices of default engine" probably belongs over here, and
the two function comments should be written to make it clear how one is a
superset of the other.

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

Done.

+  bool ShowInPrepopulatedList(const TemplateURL* template_url);
+
   // Returns whether |template_url| should be shown in the list of engines
   // most likely to be selected as a default engine. This is meant to highlight
   // the current default, as well as the other most likely choices of default
   // engine, separately from a full list of all TemplateURLs (which might be
   // very long).
   bool ShowInDefaultList(const TemplateURL* template_url);
 
   // Adds to |matches| all TemplateURLs whose keywords begin with |prefix|,
   // sorted shortest-keyword-first. If |supports_replacement_only| is true, only
   // TemplateURLs that support replacement are returned.
@@ skipping 675 matching lines @@
   // Helper class to manage the default search engine.
   DefaultSearchManager default_search_manager_;
 
   std::unique_ptr<GoogleURLTracker::Subscription>
       google_url_updated_subscription_;
 
   DISALLOW_COPY_AND_ASSIGN(TemplateURLService);
 };
 
 #endif  // COMPONENTS_SEARCH_ENGINES_TEMPLATE_URL_SERVICE_H_