Created a helper function "FindDiskBySourcePath" in DiskMountManager.

chrome/browser/chromeos/extensions/file_browser_private_api.cc

 // 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.
 
 #include "chrome/browser/chromeos/extensions/file_browser_private_api.h"
 
 #include <utility>
 
 #include "base/base64.h"
 #include "base/bind.h"
@@ skipping 90 matching lines @@
 }
 
 const DiskMountManager::Disk* GetVolumeAsDisk(const std::string& mount_path) {
   DiskMountManager* disk_mount_manager = DiskMountManager::GetInstance();
 
   DiskMountManager::MountPointMap::const_iterator mount_point_it =
       disk_mount_manager->mount_points().find(mount_path);
   if (mount_point_it == disk_mount_manager->mount_points().end())
     return NULL;
 
-  DiskMountManager::DiskMap::const_iterator disk_it =
-      disk_mount_manager->disks().find(mount_point_it->second.source_path);
+  const DiskMountManager::Disk* disk = disk_mount_manager->FindDiskBySourcePath(
+      mount_point_it->second.source_path);
 
-  if (disk_it == disk_mount_manager->disks().end() ||
-      disk_it->second->is_hidden()) {
-    return NULL;
-  }
-
-  return disk_it->second;
+  return (disk && disk->is_hidden()) ? NULL : disk;
 }
 
 base::DictionaryValue* CreateValueFromDisk(
     Profile* profile,
     const DiskMountManager::Disk* volume) {
   base::DictionaryValue* volume_info = new base::DictionaryValue();
 
   std::string mount_path;
   if (!volume->mount_path().empty()) {
     FilePath relative_mount_path;
@@ skipping 2296 matching lines @@
   gdata::GDataSystemService* system_service =
       gdata::GDataSystemServiceFactory::GetForProfile(profile_);
   if (!system_service || !system_service->file_system())
     return false;
 
   FilePath directory_path = GetVirtualPathFromURL(GURL(file_url_as_string));
   system_service->file_system()->RequestDirectoryRefresh(directory_path);
 
   return true;
 }