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

chrome/browser/prefs/pref_hash_filter.cc

Index: chrome/browser/prefs/pref_hash_filter.cc
diff --git a/chrome/browser/prefs/pref_hash_filter.cc b/chrome/browser/prefs/pref_hash_filter.cc
index e35df37edb45769367d2673f109a1097ab88b4e1..97bcc7fe2e9b007b87c39deb4a72f11b2543c8f8 100644
--- a/chrome/browser/prefs/pref_hash_filter.cc
+++ b/chrome/browser/prefs/pref_hash_filter.cc
@@ -8,7 +8,6 @@
 
 #include "base/logging.h"
 #include "base/metrics/histogram.h"
-#include "base/prefs/persistent_pref_store.h"
 #include "base/prefs/pref_service.h"
 #include "base/prefs/pref_store.h"
 #include "base/strings/string_number_conversions.h"
@@ -92,51 +91,6 @@ void PrefHashFilter::ClearResetTime(PrefService* user_prefs) {
   user_prefs->ClearPref(prefs::kPreferenceResetTime);
 }
 
-void PrefHashFilter::MigrateValues(PersistentPrefStore* source,
-                                   PersistentPrefStore* destination) {
-  bool commit_source = false;
-  bool commit_destination = false;
-
-  scoped_ptr<PrefHashStoreTransaction> transaction =
-      pref_hash_store_->BeginTransaction();
-  for (TrackedPreferencesMap::const_iterator it = tracked_paths_.begin();
-       it != tracked_paths_.end();
-       ++it) {
-    const base::Value* source_value = NULL;
-    if (source->GetValue(it->first, &source_value)) {
-      if (!destination->GetValue(it->first, NULL)) {
-        base::DictionaryValue temp_dictionary;
-        // Copy the value from |source| into a suitable place for a
-        // TrackedPreference to act on it.
-        temp_dictionary.Set(it->first, source_value->DeepCopy());
-        // Check whether the value is correct according to our MAC. May remove
-        // the value from |temp_dictionary|.
-        it->second->EnforceAndReport(&temp_dictionary, transaction.get());
-        // Now take the value as it appears in |temp_dictionary| and put it in
-        // |destination|.
-        scoped_ptr<base::Value> checked_value;
-        if (temp_dictionary.Remove(it->first, &checked_value)) {
-          destination->SetValue(it->first, checked_value.release());
-          commit_destination = true;
-        }
-      }
-      source->RemoveValue(it->first);
-      commit_source = true;
-    }
-  }
-
-  // Order these such that a crash at any point is still recoverable. We assume
-  // that they are configured such that the writes will occur on worker threads
-  // in the order that we asked for them.
-  if (commit_destination)
-    destination->CommitPendingWrite();
-  transaction.reset();
-  // If we crash here, we will just delete the values from |source| in a future
-  // invocation of MigrateValues.
-  if (commit_source)
-    source->CommitPendingWrite();
-}
-
 void PrefHashFilter::Initialize(const PrefStore& pref_store) {
   scoped_ptr<PrefHashStoreTransaction> hash_store_transaction(
       pref_hash_store_->BeginTransaction());