Add end to end test for Media galleries scan API.

chrome/browser/media_galleries/media_folder_finder.h

 // Copyright 2014 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 CHROME_BROWSER_MEDIA_GALLERIES_MEDIA_FOLDER_FINDER_H_
 #define CHROME_BROWSER_MEDIA_GALLERIES_MEDIA_FOLDER_FINDER_H_
 
 #include <map>
 #include <vector>
 
@@ skipping 20 matching lines @@
   // MediaFolderFinder has a default set of per-platform paths to scan.
   // Override in tests with SetRootsForTesting().
   explicit MediaFolderFinder(const MediaFolderFinderResultsCallback& callback);
   virtual ~MediaFolderFinder();
 
   // Start the scan.
   virtual void StartScan();
 
  private:
   friend class MediaFolderFinderTest;
+  friend class MediaGalleriesPlatformAppBrowserTest;
 
   class Worker;
   struct WorkerReply {
     WorkerReply();
     ~WorkerReply();
 
     MediaGalleryScanResult scan_result;
     std::vector<base::FilePath> new_folders;
   };
 
@@ skipping 27 matching lines @@
   // Set of roots to scan for testing.
   bool has_roots_for_testing_;
   std::vector<base::FilePath> roots_for_testing_;
 
   base::WeakPtrFactory<MediaFolderFinder> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(MediaFolderFinder);
 };
 
 #endif  // CHROME_BROWSER_MEDIA_GALLERIES_MEDIA_FOLDER_FINDER_H_