Move string files in base/ to the string subdirectory.

base/strings/stringprintf_unittest.cc

Index: base/strings/stringprintf_unittest.cc
diff --git a/base/stringprintf_unittest.cc b/base/strings/stringprintf_unittest.cc
similarity index 99%
rename from base/stringprintf_unittest.cc
rename to base/strings/stringprintf_unittest.cc
index c04b17e4c7c0413a6f43f1bbfd29fec39512f6a6..8f23082e50fceee1ad5324b62e1c33941ddaad6d 100644
--- a/base/stringprintf_unittest.cc
+++ b/base/strings/stringprintf_unittest.cc
@@ -2,10 +2,11 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include "base/strings/stringprintf.h"
+
 #include <errno.h>
 
 #include "base/basictypes.h"
-#include "base/stringprintf.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace base {