[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 133 matching lines @@
   // name part of the keyword starts with |prefix|, sorted
   // shortest-domain-name-first. If |supports_replacement_only| is true, only
   // TemplateURLs that support replacement are returned.  Does not bother
   // searching/returning keywords that would've been found with an identical
   // call to FindMatchingKeywords(); i.e., doesn't search keywords for which
   // the domain name is the keyword.
   void AddMatchingDomainKeywords(const base::string16& prefix,
                                  bool supports_replacement_only,
                                  TURLsAndMeaningfulLengths* matches);
 
+  // Returns true if the TempalteURL is prepopulated or created by policy.

[Peter Kasting, 2016/11/02 00:34:03]

Nit: TemplateURL

[ltian, 2016/11/22 21:51:41]

Done.

+  bool IsInDefaultList(const TemplateURL* url);

[Peter Kasting, 2016/11/02 00:34:03]

It seems like this is really a const member method on TemplateURL, no?  It
doesn't have anything to do with the TemplateURLService.

When moving it there, you're going to run up against ShowInDefaultList() and
show_in_default_list().  I don't think we should have all three of these
functions.  We should probably have just one.

I propose that Android's definition of the list here -- the prepopulated/policy
URLs, the current default, and a recently-used engine or two -- be what we use
on desktop, and we use that for both the dropdown in the main settings on
desktop and the top section of the search engine management dialog.  Basically,
I think we should retire the existing show_in_default_list bit.

We should probably also enforce (in all these places) that the TemplateURL
supports replacement, as ShowInDefaultList() does.

[ltian, 2016/11/22 21:51:41]

Not exist any more.

+
   // Looks up |keyword| and returns the element it maps to.  Returns NULL if
   // the keyword was not found.
   // The caller should not try to delete the returned pointer; the data store
   // retains ownership of it.
   TemplateURL* GetTemplateURLForKeyword(const base::string16& keyword);
 
   // Returns that TemplateURL with the specified GUID, or NULL if not found.
   // The caller should not try to delete the returned pointer; the data store
   // retains ownership of it.
   TemplateURL* GetTemplateURLForGUID(const std::string& sync_guid);
@@ skipping 650 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_