gdata: Implement periodic file system update checks.

chrome/browser/chromeos/extensions/file_browser_event_router.h

Index: chrome/browser/chromeos/extensions/file_browser_event_router.h
diff --git a/chrome/browser/chromeos/extensions/file_browser_event_router.h b/chrome/browser/chromeos/extensions/file_browser_event_router.h
index 4572adeff12537d16192f8d72cdce98fd83b5509..9478d80a33183e3ab903bd48cecfe55b5391e07e 100644
--- a/chrome/browser/chromeos/extensions/file_browser_event_router.h
+++ b/chrome/browser/chromeos/extensions/file_browser_event_router.h
@@ -156,6 +156,16 @@ class FileBrowserEventRouter
                       const std::string& device_path,
                       bool small);
 
+  // Returns the GDataFileSystem for the current profile.
+  gdata::GDataFileSystem* GetRemoteFileSystem() const;
+
+  // Handles requests to start and stop periodic updates on remote file system.
+  // When |start| is set to true, this function starts periodic updates only if
+  // it is not yet started; when |start| is set to false, this function stops
+  // periodic updates only if the number of outstanding update requests reaches
+  // zero.
+  void HandleRemoteUpdateRequestOnUIThread(bool start);
+
   scoped_refptr<FileWatcherDelegate> delegate_;
   WatcherMap file_watchers_;
   scoped_ptr<FileBrowserNotifications> notifications_;
@@ -165,6 +175,9 @@ class FileBrowserEventRouter
   bool current_gdata_operation_failed_;
   int last_active_gdata_operation_count_;
 
+  // Number of active update requests on the remote file system.
+  int num_remote_update_requests_;
+
   DISALLOW_COPY_AND_ASSIGN(FileBrowserEventRouter);
 };