Fix a race condition in preference metric reporting.

base/prefs/json_pref_store.h

 // Copyright (c) 2012 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.
 
 #ifndef BASE_PREFS_JSON_PREF_STORE_H_
 #define BASE_PREFS_JSON_PREF_STORE_H_
 
 #include <set>
 #include <string>
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/files/file_path.h"
 #include "base/files/important_file_writer.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/memory/scoped_vector.h"
 #include "base/message_loop/message_loop_proxy.h"
 #include "base/observer_list.h"
 #include "base/prefs/base_prefs_export.h"
 #include "base/prefs/persistent_pref_store.h"
 
 namespace base {
 class DictionaryValue;
 class FilePath;
 class SequencedWorkerPool;
 class SequencedTaskRunner;
@@ skipping 18 matching lines @@
                 base::SequencedTaskRunner* sequenced_task_runner);
 
   // PrefStore overrides:
   virtual bool GetValue(const std::string& key,
                         const base::Value** result) const OVERRIDE;
   virtual void AddObserver(PrefStore::Observer* observer) OVERRIDE;
   virtual void RemoveObserver(PrefStore::Observer* observer) OVERRIDE;
   virtual bool HasObservers() const OVERRIDE;
   virtual bool IsInitializationComplete() const OVERRIDE;
 
+  // Adds an observer that will be automatically deregistered and destroyed by
+  // ~JsonPrefStore().
+  void AddOwnedObserver(scoped_ptr<PrefStore::Observer> observer);

[gab, 2013/11/27 23:43:27]

#include base/prefs/pref_store.h

for PrefStore::Observer

[robertshield, 2013/11/28 02:54:26]

AddObserver takes a raw pointer, any reason not to make this do so as well?

[erikwright (departed), 2013/11/28 17:48:07]

Because there is a transfer of ownership.

+
   // PersistentPrefStore overrides:
   virtual bool GetMutableValue(const std::string& key,
                                base::Value** result) OVERRIDE;
   virtual void SetValue(const std::string& key, base::Value* value) OVERRIDE;
   virtual void SetValueSilently(const std::string& key,
                                 base::Value* value) OVERRIDE;
   virtual void RemoveValue(const std::string& key) OVERRIDE;
   virtual void MarkNeedsEmptyValue(const std::string& key) OVERRIDE;
   virtual bool ReadOnly() const OVERRIDE;
   virtual PrefReadError GetReadError() const OVERRIDE;
@@ skipping 18 matching lines @@
   const scoped_refptr<base::SequencedTaskRunner> sequenced_task_runner_;
 
   scoped_ptr<base::DictionaryValue> prefs_;
 
   bool read_only_;
 
   // Helper for safely writing pref data.
   base::ImportantFileWriter writer_;
 
   ObserverList<PrefStore::Observer, true> observers_;
+  ScopedVector<PrefStore::Observer> owned_observers_;
 
   scoped_ptr<ReadErrorDelegate> error_delegate_;
 
   bool initialized_;
   PrefReadError read_error_;
 
   std::set<std::string> keys_need_empty_value_;
 
   DISALLOW_COPY_AND_ASSIGN(JsonPrefStore);
 };
 
 #endif  // BASE_PREFS_JSON_PREF_STORE_H_