Remove all traces of pref hash stores after last store reset.

chrome/browser/prefs/tracked/pref_service_hash_store_contents.cc

 // Copyright 2014 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.
 
 #include "chrome/browser/prefs/tracked/pref_service_hash_store_contents.h"
 
 #include "base/prefs/pref_registry_simple.h"
 #include "base/prefs/pref_service.h"
 #include "base/prefs/scoped_user_pref_update.h"
 #include "base/values.h"
@@ skipping 67 matching lines @@
   return hash_store_id_;
 }
 
 void PrefServiceHashStoreContents::Reset() {
   DictionaryPrefUpdate update(pref_service_, prefs::kProfilePreferenceHashes);
 
   update->RemoveWithoutPathExpansion(hash_store_id_, NULL);
 
   // Remove this store's entry in the kStoreVersionsDict.
   base::DictionaryValue* version_dict;
-  if (update->GetDictionary(kStoreVersionsDict, &version_dict))
+  if (update->GetDictionary(kStoreVersionsDict, &version_dict)) {
     version_dict->RemoveWithoutPathExpansion(hash_store_id_, NULL);
+    if (version_dict->empty())
+      update->RemovePath(kStoreVersionsDict, NULL);
+  }
 
   // Remove this store's entry in the kHashOfHashesDict.
   base::DictionaryValue* hash_of_hashes_dict;
   if (update->GetDictionaryWithoutPathExpansion(kHashOfHashesDict,
                                                 &hash_of_hashes_dict)) {
     hash_of_hashes_dict->RemoveWithoutPathExpansion(hash_store_id_, NULL);
+    if (hash_of_hashes_dict->empty())
+      update->RemovePath(kHashOfHashesDict, NULL);
   }
+
+  if (update->empty())
+    pref_service_->ClearPref(prefs::kProfilePreferenceHashes);
 }
 
 bool PrefServiceHashStoreContents::IsInitialized() const {
   const base::DictionaryValue* pref_hash_dicts =
       pref_service_->GetDictionary(prefs::kProfilePreferenceHashes);
   return pref_hash_dicts->GetDictionaryWithoutPathExpansion(hash_store_id_,
                                                             NULL);
 }
 
 const base::DictionaryValue* PrefServiceHashStoreContents::GetContents() const {
@@ skipping 25 matching lines @@
 }
 
 void PrefServiceHashStoreContents::SetSuperMac(const std::string& super_mac) {
   PrefServiceMutableDictionary(kHashOfHashesDict, pref_service_)
       ->SetStringWithoutPathExpansion(hash_store_id_, super_mac);
 }
 
 void PrefServiceHashStoreContents::CommitPendingWrite() {
   pref_service_->CommitPendingWrite();
 }