Add support for refreshing contents of providers which don't support watchers.

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.
 [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 as well
   // as in case of errors when calling methods of the API. For success,
@@ skipping 526 matching lines @@
     // <code>fileSystemId</code>.
     static void get(DOMString fileSystemId, GetCallback callback);
 
     // Notifies about changes in the watched directory at
     // <code>observedPath</code> in <code>recursive</code> mode. If the file
     // system is mounted with <code>supportsNofityTag</code>, then
     // <code>tag</code> must be provided, and all changes since the last
     // notification always reported, even if the system was shutdown. The last
     // tag can be obtained with $(ref:getAll).
     //
+    // To use, the <code>file_system_provider.notify</code> manifest option
+    // must be set to true.
+    //
     // Value of <code>tag</code> can be any string which is unique per call,
     // so it's possible to identify the last registered notification. Eg. if
     // the providing extension starts after a reboot, and the last registered
     // notification's tag is equal to "123", then it should call $(ref:notify)
     // for all changes which happened since the change tagged as "123". It
     // cannot be an empty string.
     //
     // Not all providers are able to provide a tag, but if the file system has
     // a changelog, then the tag can be eg. a change number, or a revision
     // number.
@@ skipping 173 matching lines @@
     // Raised when executing an action for a file or a directory is requested.
     // After the action is completed, <code>successCallback</code> must be
     // called. On error, <code>errorCallback</code> must be called.
     [maxListeners=1, nodoc] static void onExecuteActionRequested(
       ExecuteActionRequestedOptions options,
       ProviderSuccessCallback successCallback,
       ProviderErrorCallback errorCallback);
   };
 };