Revert of Improve computation of PrefHashCalculator::legacy_device_id_instance_.

chrome/browser/prefs/pref_hash_calculator.h

 // Copyright 2013 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 CHROME_BROWSER_PREFS_PREF_HASH_CALCULATOR_H_
 #define CHROME_BROWSER_PREFS_PREF_HASH_CALCULATOR_H_
 
 #include <string>
 
 #include "base/basictypes.h"
 #include "base/callback.h"
-#include "base/lazy_instance.h"
 #include "base/memory/scoped_ptr.h"
 
 namespace base {
 class Value;
 }  // namespace base
 
 // Calculates and validates preference value hashes.
 class PrefHashCalculator {
  public:
   enum ValidationResult {
@@ skipping 43 matching lines @@
   const std::string seed_;
   const std::string device_id_;
 
   // The raw device id from which the legacy device id will be derived if
   // required.
   const std::string raw_device_id_;
 
   const GetLegacyDeviceIdCallback get_legacy_device_id_callback_;
 
   // A cache for the legacy device id which is hard to compute and thus lazily
-  // computed when/if required. The same instance is used across all
-  // PrefHashCalculators.
-  static base::LazyInstance<scoped_ptr<const std::string> >::Leaky
-      legacy_device_id_instance_;
+  // computed when/if required (computing the original value for this instance
+  // is allowed in const methods).
+  mutable scoped_ptr<const std::string> legacy_device_id_instance_;
 
   DISALLOW_COPY_AND_ASSIGN(PrefHashCalculator);
 };
 
 #endif  // CHROME_BROWSER_PREFS_PREF_HASH_CALCULATOR_H_