Revert of Move JoinString to the base namespace

components/search_engines/default_search_pref_migration_unittest.cc

Index: components/search_engines/default_search_pref_migration_unittest.cc
diff --git a/components/search_engines/default_search_pref_migration_unittest.cc b/components/search_engines/default_search_pref_migration_unittest.cc
index 73d9d0bf0dff92f4b33e97507762f988bde2048c..6d1b6eafe6dd37846cda72f121e5d836e0f641de 100644
--- a/components/search_engines/default_search_pref_migration_unittest.cc
+++ b/components/search_engines/default_search_pref_migration_unittest.cc
@@ -91,7 +91,7 @@
     GURL icon_gurl = t_url->favicon_url();
     if (!icon_gurl.is_empty())
       icon_url = icon_gurl.spec();
-    encodings = base::JoinString(t_url->input_encodings(), ";");
+    encodings = JoinString(t_url->input_encodings(), ';');
     short_name = base::UTF16ToUTF8(t_url->short_name());
     keyword = base::UTF16ToUTF8(t_url->keyword());
     id_string = base::Int64ToString(t_url->id());