Media Galleries API: Fix MediaGalleriesPreferences finders race.

chrome/browser/media_galleries/fileapi/picasa_finder.cc

 // Copyright 2013 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/media_galleries/fileapi/picasa_finder.h"
 
 #include "base/base_paths.h"
 #include "base/bind.h"
 #include "base/file_util.h"
 #include "base/path_service.h"
@@ skipping 28 matching lines @@
 
   // Verify actual existence
   if (!base::DirectoryExists(path))
     path.clear();
 
   return path;
 }
 
 void FinishOnOriginalThread(const PicasaFinder::DeviceIDCallback& callback,
                             const base::FilePath& database_path) {
-  if (!database_path.empty())
-    callback.Run(StorageInfo::MakeDeviceId(StorageInfo::PICASA,
-                                           database_path.AsUTF8Unsafe()));
+  std::string device_id;
+  if (!database_path.empty()) {
+    device_id = StorageInfo::MakeDeviceId(StorageInfo::PICASA,
+                                          database_path.AsUTF8Unsafe());
+  }
+  callback.Run(device_id);
 }
 
 }  // namespace
 
 void PicasaFinder::FindPicasaDatabase(
     const PicasaFinder::DeviceIDCallback& callback) {
   content::BrowserThread::PostTaskAndReplyWithResult(
       content::BrowserThread::FILE,
       FROM_HERE,
       base::Bind(&FindPicasaDatabaseOnFileThread),
       base::Bind(&FinishOnOriginalThread, callback));
 }
 
 }  // namespace picasa