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

components/search_engines/template_url_service.h

Index: components/search_engines/template_url_service.h
diff --git a/components/search_engines/template_url_service.h b/components/search_engines/template_url_service.h
index da7c5169a0f09b3d1ca09bff53e07c62fefc88f4..0657aa9e716db2c9eacba16fe4a38871f9c6747d 100644
--- a/components/search_engines/template_url_service.h
+++ b/components/search_engines/template_url_service.h
@@ -151,6 +151,9 @@ class TemplateURLService : public WebDataServiceConsumer,
                                  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