Revert of Move JoinString to the base namespace

ui/app_list/search/tokenized_string_char_iterator_unittest.cc

Index: ui/app_list/search/tokenized_string_char_iterator_unittest.cc
diff --git a/ui/app_list/search/tokenized_string_char_iterator_unittest.cc b/ui/app_list/search/tokenized_string_char_iterator_unittest.cc
index d5fe1b30644d06a8909212b38639f9e4129415df..38460145e01693e83dc05955b3a0705bef9968a3 100644
--- a/ui/app_list/search/tokenized_string_char_iterator_unittest.cc
+++ b/ui/app_list/search/tokenized_string_char_iterator_unittest.cc
@@ -48,7 +48,7 @@
     iter.NextChar();
   }
 
-  EXPECT_EQ(expects, base::JoinString(results, " "));
+  EXPECT_EQ(expects, JoinString(results, ' '));
   TestBeyondTheEnd(&iter);
 }
 
@@ -62,7 +62,7 @@
     iter.NextToken();
   }
 
-  EXPECT_EQ(expects, base::JoinString(results, " "));
+  EXPECT_EQ(expects, JoinString(results, ' '));
   TestBeyondTheEnd(&iter);
 }
 
@@ -80,7 +80,7 @@
     iter.NextToken();
   }
 
-  EXPECT_EQ(expects, base::JoinString(results, " "));
+  EXPECT_EQ(expects, JoinString(results, ' '));
   TestBeyondTheEnd(&iter);
 }