Make largest_changestamp setter/getter asynchronous.

chrome/browser/chromeos/drive/drive_file_system_interface.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 CHROME_BROWSER_CHROMEOS_DRIVE_DRIVE_FILE_SYSTEM_INTERFACE_H_
 #define CHROME_BROWSER_CHROMEOS_DRIVE_DRIVE_FILE_SYSTEM_INTERFACE_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 54 matching lines @@
 // Used to open files from the file system. |file_path| is the path on the local
 // file system for the opened file.
 typedef base::Callback<void(DriveFileError error,
                             const FilePath& file_path)> OpenFileCallback;
 
 // Used to get available space for the account from Drive.
 typedef base::Callback<void(DriveFileError error,
                             int64 bytes_total,
                             int64 bytes_used)> GetAvailableSpaceCallback;
 
+// Used to get drive filesystem metadata.
+typedef base::Callback<void(const DriveFileSystemMetadata&)>
+    GetFilesystemMetadataCallback;
+
 // Drive file system abstraction layer.
 // The interface is defined to make DriveFileSystem mockable.
 class DriveFileSystemInterface {
  public:
   virtual ~DriveFileSystemInterface() {}
 
   // Initializes the object. This function should be called before any
   // other functions.
   virtual void Initialize() = 0;
 
@@ skipping 249 matching lines @@
   // |file_content_path| into the cache.
   //
   // |callback| will be called on the UI thread upon completion of operation.
   // |callback| must not be null.
   virtual void AddUploadedFile(const FilePath& directory_path,
                                scoped_ptr<google_apis::ResourceEntry> doc_entry,
                                const FilePath& file_content_path,
                                const FileOperationCallback& callback) = 0;
 
   // Returns miscellaneous metadata of the file system like the largest
-  // timestamp. Used in chrome:drive-internals.
-  virtual DriveFileSystemMetadata GetMetadata() const = 0;
+  // timestamp. Used in chrome:drive-internals. |callback| must not be null.
+  virtual void GetMetadata(
+      const GetFilesystemMetadataCallback& callback) = 0;
 
   // Reloads the file system feeds from the server.
   virtual void Reload() = 0;
 };
 
 }  // namespace drive
 
 #endif  // CHROME_BROWSER_CHROMEOS_DRIVE_DRIVE_FILE_SYSTEM_INTERFACE_H_