[fsp] Add support for closing files.

chrome/common/extensions/api/file_system_provider.idl

 // Copyright 2013 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.
 
 // Use the <code>chrome.fileSystemProvider</code> API to create file systems,
 // that can be accessible from the file manager on Chrome OS.
 [platforms=("chromeos"),
  implemented_in="chrome/browser/chromeos/extensions/file_system_provider/file_system_provider_api.h"]
 namespace fileSystemProvider {
   // Error codes used by providing extensions in response to requests. For
@@ skipping 126 matching lines @@
     // Raised when opening a file at <code>filePath</code> is requested.
     // If <code>create</code> is set to <code>true</code> and the file does not
     // exist, then it should be created.
     [maxListeners=1] static void onOpenFileRequested(
         long fileSystemId,
         DOMString filePath,
         OpenFileMode mode,
         boolean create,
         ProviderSuccessCallback successCallback,
         ProviderErrorCallback errorCallback);
+
+    // Raised when opening a file previously opened with <code>openRequestId
+    // </code> is requested to be closed.
+    [maxListeners=1] static void onCloseFileRequested(
+        long fileSystemId,
+        long openRequestId,
+        ProviderSuccessCallback successCallback,
+        ProviderErrorCallback errorCallback);
   };
 };