Multi-strategy based tracking.

chrome/browser/prefs/tracked_preference_helper.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_TRACKED_PREFERENCE_HELPER_H_
+#define CHROME_BROWSER_PREFS_TRACKED_PREFERENCE_HELPER_H_
+
+#include "base/macros.h"
+#include "chrome/browser/prefs/pref_hash_store.h"
+
+// A TrackedPreferenceHelper is a helper class for TrackedPreference which
+// handles decision making and reporting for TrackedPreference's
+// implementations.
+class TrackedPreferenceHelper {
+ public:
+  // Enforcement levels are defined in order of intensity; the next level always
+  // implies the previous one and more.
+  enum EnforcementLevel {

[erikwright (departed), 2014/01/17 20:23:01]

I would probably put this in its own file. It doesn't make sense for
chrome_pref_service_factory to be aware of TrackedPreferenceHelper.

[gab, 2014/01/17 21:32:01]

Put it back in PrefHashFilter.

+    NO_ENFORCEMENT,
+    ENFORCE,
+    ENFORCE_NO_SEEDING,
+    ENFORCE_NO_SEEDING_NO_MIGRATION,
+    // ENFORCE_ALL must always remain last; it is meant to be used when the
+    // desired level is underdetermined and the caller wants to enforce the
+    // strongest level to be safe.
+    ENFORCE_ALL
+  };
+
+  enum ResetAction {
+    DONT_RESET,
+    // WANTED_RESET is reported when DO_RESET would have been reported but the
+    // current |enforcement_level| doesn't allow a reset for the detected state.
+    WANTED_RESET,
+    DO_RESET,
+  };
+
+  TrackedPreferenceHelper(const std::string& pref_path,
+                          size_t reporting_id,
+                          size_t reporting_ids_count,
+                          EnforcementLevel enforcement_level);
+
+  // Returns a ResetAction stating whether a reset is desired (DO_RESET) based
+  // on observing |value_state| or not (DONT_RESET). |allow_changes_|,
+  // |allow_seeding_|, and |allow_migration_| make the decision softer in favor
+  // of WANTED_RESET over DO_RESET in various scenarios.
+  ResetAction GetAction(PrefHashStore::ValueState value_state) const;
+
+  // Reports |value_state| via UMA under |reporting_id_|.
+  void ReportValidationResult(PrefHashStore::ValueState value_state) const;
+
+  // Reports |reset_action| via UMA under |reporting_id_|.
+  void ReportAction(ResetAction reset_action) const;
+
+  // Reports, via UMA, the |count| of split preference entries that were
+  // considered invalid in a CHANGED event.
+  void ReportSplitPreferenceChangedCount(size_t count) const;
+
+ private:
+  const std::string pref_path_;
+
+  const size_t reporting_id_;
+  const size_t reporting_ids_count_;
+
+  // Allow setting changes.
+  const bool allow_changes_;
+  // Allow seeding unknown values for atomic preferences.
+  const bool allow_seeding_;
+  // Allow migration of values validated by the old MAC algorithm.
+  const bool allow_migration_;
+
+  DISALLOW_COPY_AND_ASSIGN(TrackedPreferenceHelper);
+};
+
+#endif  // CHROME_BROWSER_PREFS_TRACKED_PREFERENCE_HELPER_H_