Make extensions DSE persistent in browser prefs

components/search_engines/template_url_prepopulate_data.h

Index: components/search_engines/template_url_prepopulate_data.h
diff --git a/components/search_engines/template_url_prepopulate_data.h b/components/search_engines/template_url_prepopulate_data.h
index 4276908b0e66fc49f8684b0bd9de2f0824fd1d18..c257c7dcc17ed81eddd535ebfbf6e167f0e224cb 100644
--- a/components/search_engines/template_url_prepopulate_data.h
+++ b/components/search_engines/template_url_prepopulate_data.h
@@ -42,6 +42,10 @@ std::vector<std::unique_ptr<TemplateURLData>> GetPrepopulatedEngines(
     PrefService* prefs,
     size_t* default_search_provider_index);
 
+// Find the prepopulated search engine with the given id.
+std::unique_ptr<TemplateURLData> GetPrepopulatedEngine(PrefService* prefs,
+                                                       int prepopulated_id);
+
 #if defined(OS_ANDROID)
 // Returns the prepopulated URLs associated with |locale|, if it differs from
 // the current country.  |locale| should be a two-character uppercase ISO 3166-1