[Metrics] Move CachingPermutedEntropyProvider into the variations component.

chrome/common/metrics/caching_permuted_entropy_provider.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_COMMON_METRICS_CACHING_PERMUTED_ENTROPY_PROVIDER_H_
-#define CHROME_COMMON_METRICS_CACHING_PERMUTED_ENTROPY_PROVIDER_H_
-
-#include "base/basictypes.h"
-#include "base/compiler_specific.h"
-#include "base/threading/thread_checker.h"
-#include "chrome/common/metrics/proto/permuted_entropy_cache.pb.h"
-#include "components/variations/entropy_provider.h"
-
-class PrefService;
-class PrefRegistrySimple;
-
-namespace metrics {
-
-// CachingPermutedEntropyProvider is an entropy provider that uses the same
-// algorithm as the PermutedEntropyProvider, but caches the results in Local
-// State between runs.
-class CachingPermutedEntropyProvider : public PermutedEntropyProvider {
- public:
-  // Creates a CachingPermutedEntropyProvider using the given |local_state|
-  // prefs service with the specified |low_entropy_source|, which should have a
-  // value in the range of [0, low_entropy_source_max).
-  CachingPermutedEntropyProvider(PrefService* local_state,
-                                 uint16 low_entropy_source,
-                                 size_t low_entropy_source_max);
-  virtual ~CachingPermutedEntropyProvider();
-
-  // Registers pref keys used by this class in the Local State pref registry.
-  static void RegisterPrefs(PrefRegistrySimple* registry);
-
-  // Clears the cache in local state. Should be called when the low entropy
-  // source value gets reset.
-  static void ClearCache(PrefService* local_state);
-
- private:
-  // PermutedEntropyProvider overrides:
-  virtual uint16 GetPermutedValue(uint32 randomization_seed) const OVERRIDE;
-
-  // Reads the cache from local state.
-  void ReadFromLocalState() const;
-
-  // Updates local state with the state of the cache.
-  void UpdateLocalState() const;
-
-  // Adds |randomization_seed| -> |value| to the cache.
-  void AddToCache(uint32 randomization_seed, uint16 value) const;
-
-  // Finds the value corresponding to |randomization_seed|, setting |value| and
-  // returning true if found.
-  bool FindValue(uint32 randomization_seed, uint16* value) const;
-
-  base::ThreadChecker thread_checker_;
-  PrefService* local_state_;
-  mutable PermutedEntropyCache cache_;
-
-  DISALLOW_COPY_AND_ASSIGN(CachingPermutedEntropyProvider);
-};
-
-}  // namespace metrics
-
-#endif  // CHROME_COMMON_METRICS_CACHING_PERMUTED_ENTROPY_PROVIDER_H_