Move string files in base/ to the string subdirectory.

base/strings/stringprintf.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef BASE_STRINGPRINTF_H_
-#define BASE_STRINGPRINTF_H_
+#ifndef BASE_STRINGS_STRINGPRINTF_H_
+#define BASE_STRINGS_STRINGPRINTF_H_
 
 #include <stdarg.h>   // va_list
 
 #include <string>
 
 #include "base/base_export.h"
 #include "base/compiler_specific.h"
 
 namespace base {
 
@@ skipping 35 matching lines @@
 BASE_EXPORT void StringAppendV(std::string* dst, const char* format, va_list ap)
     PRINTF_FORMAT(2, 0);
 #if !defined(OS_ANDROID)
 BASE_EXPORT void StringAppendV(std::wstring* dst,
                                const wchar_t* format, va_list ap)
     WPRINTF_FORMAT(2, 0);
 #endif
 
 }  // namespace base
 
-#endif  // BASE_STRINGPRINTF_H_
+#endif  // BASE_STRINGS_STRINGPRINTF_H_