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

chrome/browser/prefs/tracked/pref_service_hash_store_contents.cc

Index: chrome/browser/prefs/tracked/pref_service_hash_store_contents.cc
diff --git a/chrome/browser/prefs/tracked/pref_service_hash_store_contents.cc b/chrome/browser/prefs/tracked/pref_service_hash_store_contents.cc
index 103e3501af6b8ebd1cef9b5df02775de66667605..e121df367879be41fddc2c3ca17231a59e6f013c 100644
--- a/chrome/browser/prefs/tracked/pref_service_hash_store_contents.cc
+++ b/chrome/browser/prefs/tracked/pref_service_hash_store_contents.cc
@@ -85,15 +85,23 @@ void PrefServiceHashStoreContents::Reset() {
 
   // 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 {