Introduce a new framework for back-and-forth tracked/protected preferences migration.

chrome/browser/prefs/pref_hash_filter.h

Index: chrome/browser/prefs/pref_hash_filter.h
diff --git a/chrome/browser/prefs/pref_hash_filter.h b/chrome/browser/prefs/pref_hash_filter.h
index 7cb08313d0615faf26bb9bccdc124412af3fdcb0..8d5db64f95103b0cd0fa16438b76ba951a96505e 100644
--- a/chrome/browser/prefs/pref_hash_filter.h
+++ b/chrome/browser/prefs/pref_hash_filter.h
@@ -18,7 +18,6 @@
 #include "chrome/browser/prefs/pref_hash_store.h"
 #include "chrome/browser/prefs/tracked/tracked_preference.h"
 
-class PersistentPrefStore;
 class PrefService;
 class PrefStore;
 
@@ -84,15 +83,6 @@ class PrefHashFilter : public PrefFilter {
   // |pref_store|.
   void Initialize(const PrefStore& pref_store);
 
-  // Migrates protected values from |source| to |destination|. Values are
-  // migrated if they are protected according to this filter's configuration,
-  // the corresponding key has no value in |destination|, and the value in
-  // |source| is trusted according to this filter's PrefHashStore. Regardless of
-  // the state of |destination| or the trust status, the protected values will
-  // be removed from |source|.
-  void MigrateValues(PersistentPrefStore* source,
-                     PersistentPrefStore* destination);
-
   // PrefFilter implementation.
   virtual bool FilterOnLoad(base::DictionaryValue* pref_store_contents)
       OVERRIDE;