[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);
 
-  // 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).
+  // Returns whether the engine is a "pre-existing" engine, either from the
+  // prepopulate list or created by policy.
+  bool IsPrepopulatedOrCreatedByPolicy(const TemplateURL* template_url);
+
+  // Returns whether |template_url| is the current default or return true for
+  // IsPrepopulatedOrCreatedByPolicy(). 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).

[Peter Kasting, 2016/11/30 07:36:49]

Nit: I still would revert this comment to the original one on this function,
which seems clearer.

   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.
   void AddMatchingKeywords(const base::string16& prefix,
                            bool supports_replacement_only,
                            TURLsAndMeaningfulLengths* matches);
 
   // Adds to |matches| all TemplateURLs for search engines with the domain
@@ skipping 670 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_