Add a rand_util method for generating a random string.

base/rand_util.h

 // Copyright (c) 2011 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_RAND_UTIL_H_
 #define BASE_RAND_UTIL_H_
 #pragma once
 
+#include <string>
+
 #include "base/base_api.h"
 #include "base/basictypes.h"
 
 namespace base {
 
 // Returns a random number in range [0, kuint64max]. Thread-safe.
 BASE_API uint64 RandUint64();
 
 // Returns a random number between min and max (inclusive). Thread-safe.
 BASE_API int RandInt(int min, int max);
 
 // Returns a random number in range [0, max).  Thread-safe.
 //
 // Note that this can be used as an adapter for std::random_shuffle():
 // Given a pre-populated |std::vector<int> myvector|, shuffle it as
 //   std::random_shuffle(myvector.begin(), myvector.end(), base::RandGenerator);
 BASE_API uint64 RandGenerator(uint64 max);
 
 // Returns a random double in range [0, 1). Thread-safe.
 BASE_API double RandDouble();
 
+// Returns a random string of the specified length.
+BASE_API std::string RandBytesAsString(size_t length);
+
 }  // namespace base
 
 #endif  // BASE_RAND_UTIL_H_