[SystemInfo API] Rewrite storage info provider using storage monitor impl.

chrome/common/extensions/api/experimental_system_info_storage.idl

 // 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.
 
 namespace experimental.systemInfo.storage {
 
   enum StorageUnitType {
     // The storage has fixed media, e.g. hard disk or SSD.
     fixed,
     // The storage is removable, e.g. USB flash drive.
     removable,
     // The storage type is unknown.
     unknown
   };
 
   dictionary StorageUnitInfo {
-    // The unique id of the storage unit.
+    // The unique storage id. It is persistent between storage attachments.
     DOMString id;
+    // The mount path of the storage unit.
+    DOMString location;
     // The media type of the storage unit.
     StorageUnitType type;
     // The total amount of the storage space, in bytes.
     double capacity;
     // The available amount of the storage space, in bytes.
     double availableCapacity;
   };
 
   dictionary StorageChangeInfo {
     // The uniue id of the storage unit already changed.
@@ skipping 40 matching lines @@
 
     // Fired when a new removable storage is attached to the system.
     static void onAttached(StorageUnitInfo info);
 
     // Fired when a removable storage is detached from the system.
     static void onDetached(DOMString id);
   };
  
 };