ChromeOS: fix crash in HashWallpaperFilesIdStr.

chromeos/cryptohome/system_salt_getter.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 CHROMEOS_CRYPTOHOME_SYSTEM_SALT_GETTER_H_
 #define CHROMEOS_CRYPTOHOME_SYSTEM_SALT_GETTER_H_
 
 #include <stdint.h>
 
 #include <string>
@@ skipping 21 matching lines @@
   static void Shutdown();
   static SystemSaltGetter* Get();
 
   // Converts |salt| to a hex encoded string.
   static std::string ConvertRawSaltToHexString(const RawSalt& salt);
 
   // Returns system hash in hex encoded ascii format. Note: this may return
   // an empty string (e.g. errors in D-Bus layer)
   void GetSystemSalt(const GetSystemSaltCallback& callback);
 
+  // Adds another callback to be called when system salt is received.
+  // (If system salt is available, closure will be called immediately).
+  void AddOnSystemSaltReady(const base::Closure& closure);
+
   // Returns pointer to binary system salt if it is already known.
   // Returns nullptr if system salt is not known.
   const RawSalt* GetRawSalt() const;
 
   // This is for browser tests API.
   void SetRawSaltForTesting(const RawSalt& raw_salt);
 
  protected:
   SystemSaltGetter();
   ~SystemSaltGetter();
 
  private:
   // Used to implement GetSystemSalt().
   void DidWaitForServiceToBeAvailable(const GetSystemSaltCallback& callback,
                                       bool service_is_available);
   void DidGetSystemSalt(const GetSystemSaltCallback& callback,
                         DBusMethodCallStatus call_status,
                         const RawSalt& system_salt);
 
   RawSalt raw_salt_;
   std::string system_salt_;
 
+  // List of callbacks waiting for system salt ready event.
+  std::vector<base::Closure> on_system_salt_ready_;
+
   base::WeakPtrFactory<SystemSaltGetter> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(SystemSaltGetter);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROMEOS_CRYPTOHOME_SYSTEM_SALT_GETTER_H_