[fsp] Add support for truncating files.

chrome/browser/chromeos/file_system_provider/provided_file_system_interface.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_CHROMEOS_FILE_SYSTEM_PROVIDER_PROVIDED_FILE_SYSTEM_INTERFACE_H_
 #define CHROME_BROWSER_CHROMEOS_FILE_SYSTEM_PROVIDER_PROVIDED_FILE_SYSTEM_INTERFACE_H_
 
 #include <string>
 
 #include "base/callback.h"
@@ skipping 118 matching lines @@
       const base::FilePath& target_path,
       const fileapi::AsyncFileUtil::StatusCallback& callback) = 0;
 
   // Requests moving an entry (recursively in case of a directory) within the
   // same file system.
   virtual void MoveEntry(
       const base::FilePath& source_path,
       const base::FilePath& target_path,
       const fileapi::AsyncFileUtil::StatusCallback& callback) = 0;
 
+  // Requests truncating a file to the desired length.
+  virtual void Truncate(
+      const base::FilePath& file_path,
+      int64 length,
+      const fileapi::AsyncFileUtil::StatusCallback& callback) = 0;
+
   // Returns a provided file system info for this file system.
   virtual const ProvidedFileSystemInfo& GetFileSystemInfo() const = 0;
 
   // Returns a request manager for the file system.
   virtual RequestManager* GetRequestManager() = 0;
 
   // Returns a weak pointer to this object.
   virtual base::WeakPtr<ProvidedFileSystemInterface> GetWeakPtr() = 0;
 };
 
 }  // namespace file_system_provider
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_FILE_SYSTEM_PROVIDER_PROVIDED_FILE_SYSTEM_INTERFACE_H_