Use a direct include of strings headers in base/.

base/json/json_writer.cc

 // 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.
 
 #include "base/json/json_writer.h"
 
 #include <cmath>
 
 #include "base/json/string_escape.h"
 #include "base/logging.h"
-#include "base/stringprintf.h"
 #include "base/strings/string_number_conversions.h"
+#include "base/strings/stringprintf.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/values.h"
 
 namespace base {
 
 #if defined(OS_WIN)
 static const char kPrettyPrintLineEnding[] = "\r\n";
 #else
 static const char kPrettyPrintLineEnding[] = "\n";
 #endif
@@ skipping 201 matching lines @@
   JsonDoubleQuote(UTF8ToUTF16(str), true, json_string_);
 }
 
 void JSONWriter::IndentLine(int depth) {
   // It may be faster to keep an indent string so we don't have to keep
   // reallocating.
   json_string_->append(std::string(depth * 3, ' '));
 }
 
 }  // namespace base