Expand the JsonPrefStore's interface to allow for an alternate filename to be specified.

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>
 
@@ skipping 25 matching lines @@
     : public PersistentPrefStore,
       public base::ImportantFileWriter::DataSerializer,
       public base::SupportsWeakPtr<JsonPrefStore> {
  public:
   // Returns instance of SequencedTaskRunner which guarantees that file
   // operations on the same file will be executed in sequenced order.
   static scoped_refptr<base::SequencedTaskRunner> GetTaskRunnerForFile(
       const base::FilePath& pref_filename,
       base::SequencedWorkerPool* worker_pool);
 
-  // |sequenced_task_runner| is must be a shutdown-blocking task runner, ideally
-  // created by GetTaskRunnerForFile() method above.
+  // Same as the constructor below with no alternate filename.
   JsonPrefStore(const base::FilePath& pref_filename,
                 base::SequencedTaskRunner* sequenced_task_runner,
                 scoped_ptr<PrefFilter> pref_filter);
 
+  // |sequenced_task_runner| must be a shutdown-blocking task runner, ideally
+  // created by the GetTaskRunnerForFile() method above.
+  // |pref_filename| is the path to the file to read prefs from.
+  // |pref_alternate_filename| is the path to an alternate file which the
+  // desired prefs may have previously been written to. If |pref_filename|
+  // doesn't exist and |pref_alternate_filename| does, |pref_alternate_filename|
+  // will be moved to |pref_filename| before the read occurs.
+  JsonPrefStore(const base::FilePath& pref_filename,
+                const base::FilePath& pref_alternate_filename,
+                base::SequencedTaskRunner* sequenced_task_runner,
+                scoped_ptr<PrefFilter> pref_filter);
+
   // 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;
 
   // PersistentPrefStore overrides:
   virtual bool GetMutableValue(const std::string& key,
@@ skipping 46 matching lines @@
   // potentially been intercepted and modified by |pref_filter_|.
   // |initialization_successful| is pre-determined by OnFileRead() and should
   // be used when reporting OnInitializationCompleted().
   // |schedule_write| indicates whether a write should be immediately scheduled
   // (typically because the |pref_filter_| has already altered the |prefs|) --
   // this will be ignored if this store is read-only.
   void FinalizeFileRead(bool initialization_successful,
                         scoped_ptr<base::DictionaryValue> prefs,
                         bool schedule_write);
 
-  base::FilePath path_;
+  const base::FilePath path_;
+  const base::FilePath alternate_path_;
   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_;
 
   scoped_ptr<PrefFilter> pref_filter_;
   ObserverList<PrefStore::Observer, true> observers_;
 
   scoped_ptr<ReadErrorDelegate> error_delegate_;
 
   bool initialized_;
   bool filtering_in_progress_;
   PrefReadError read_error_;
 
   std::set<std::string> keys_need_empty_value_;
 
   DISALLOW_COPY_AND_ASSIGN(JsonPrefStore);
 };
 
 #endif  // BASE_PREFS_JSON_PREF_STORE_H_