Revert of Move JoinString to the base namespace

base/test/launcher/test_launcher_ios.cc

Index: base/test/launcher/test_launcher_ios.cc
diff --git a/base/test/launcher/test_launcher_ios.cc b/base/test/launcher/test_launcher_ios.cc
index 3179bb3af371f77a2580cf68d47331d6d0ae7b33..ecd31aedf5d00cb3754b0c1d4220b65e1dce3e51 100644
--- a/base/test/launcher/test_launcher_ios.cc
+++ b/base/test/launcher/test_launcher_ios.cc
@@ -121,7 +121,7 @@
     base::CommandLine cmd_line(dir_exe_.AppendASCII(test_name_ + ".app"));
     cmd_line.AppendSwitchPath(switches::kTestLauncherOutput, output_file);
     cmd_line.AppendSwitchASCII(base::kGTestFilterFlag,
-                               base::JoinString(test_names, ":"));
+                               JoinString(test_names, ":"));
     return cmd_line;
   }