Multi-strategy based tracking.

chrome/browser/prefs/tracked_preference.h

+// Copyright 2013 The Chromium Authors. All rights reserved.

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

Update this in all your new files. It's 2014, baby.

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

Done.

+// 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_H_
+#define CHROME_BROWSER_PREFS_TRACKED_PREFERENCE_H_
+
+class PrefHashStore;
+
+namespace base {
+class DictionaryValue;
+class Value;
+}
+
+// A TrackedPreference is a pure-virtual class whose subclasses are responsible

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

I think it's atypical to describe a class's OO characteristics like this. More
typically you would say something like:

// A TrackedPreference tracks changes to an individual preference, reporting and
reacting to them according to preference-specific and browser-wide policies.

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

Done.

+// for handling hash storage and pref enforcement with the help of decisions
+// made via queries to TrackedPreferenceHelper.
+class TrackedPreference {
+ public:
+  virtual ~TrackedPreference() {}
+
+  // Stores a new hash in |pref_hash_store| for this preference's |value|.

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

The method name and comment are somewhat misleading. This could store multiple
hashes, too.

How about OnValueChanged?

// Updates |pref_hash_store| to reflect the preference's new value |value|.

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

Done.

+  virtual void StoreHash(const base::Value* value,
+                         PrefHashStore* pref_hash_store) const = 0;
+
+  // Enforces that the value of this tracked preference in |pref_store_contents|

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

Enforces -> Verifies...

// ... Responds to verification failures according to preference-specific and
browser-wide policy and reports results to via UMA.

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

Done.

+  // is valid according to |pref_hash_store|; otherwise discarding the value in
+  // |pref_store_contents|. Reports on its findings via UMA.
+  virtual void EnforceAndReport(
+      PrefHashStore* pref_hash_store,
+      base::DictionaryValue* pref_store_contents) const = 0;
+};
+
+#endif  // CHROME_BROWSER_PREFS_TRACKED_PREFERENCE_H_