gdata: Implement periodic file system update checks.

chrome/browser/chromeos/gdata/gdata_file_system.h

Index: chrome/browser/chromeos/gdata/gdata_file_system.h
diff --git a/chrome/browser/chromeos/gdata/gdata_file_system.h b/chrome/browser/chromeos/gdata/gdata_file_system.h
index c963adc4545962b8d62a31b362e30ad0933a11fc..81514fbe567f85289f581e57c123dddccf3baef8 100644
--- a/chrome/browser/chromeos/gdata/gdata_file_system.h
+++ b/chrome/browser/chromeos/gdata/gdata_file_system.h
@@ -18,6 +18,7 @@
 #include "base/memory/weak_ptr.h"
 #include "base/message_loop.h"
 #include "base/platform_file.h"
+#include "base/timer.h"
 #include "base/synchronization/lock.h"
 #include "base/threading/sequenced_worker_pool.h"
 #include "chrome/browser/chromeos/gdata/find_entry_delegate.h"
@@ -175,6 +176,15 @@ class GDataFileSystemInterface {
   virtual void AddObserver(Observer* observer) = 0;
   virtual void RemoveObserver(Observer* observer) = 0;
 
+  // Requests to start periodic updates.
+  // This function only starts periodic updates if it is not yet started.
+  virtual void RequestStartUpdates() = 0;
+
+  // Requests to stop periodic updates.
+  // This function only stops periodic updates if the number of outstanding
+  // update requests reaches zero.
+  virtual void RequestStopUpdates() = 0;
+
   // Enum defining origin of a cached file.
   enum CachedFileOrigin {
     CACHED_FILE_FROM_SERVER = 0,
@@ -400,6 +410,8 @@ class GDataFileSystem : public GDataFileSystemInterface,
   virtual void Initialize() OVERRIDE;
   virtual void AddObserver(Observer* observer) OVERRIDE;
   virtual void RemoveObserver(Observer* observer) OVERRIDE;
+  virtual void RequestStartUpdates() OVERRIDE;
+  virtual void RequestStopUpdates() OVERRIDE;
   virtual void Authenticate(const AuthStatusCallback& callback) OVERRIDE;
   virtual void FindEntryByResourceIdSync(const std::string& resource_id,
                                          FindEntryDelegate* delegate) OVERRIDE;
@@ -1303,6 +1315,9 @@ class GDataFileSystem : public GDataFileSystemInterface,
       bool to_mount,
       const SetMountedStateCallback& callback);
 
+  // Checks for updates on the server.
+  void CheckForUpdates();
+
   scoped_ptr<GDataRootDirectory> root_;
 
   // This guards regular states.
@@ -1333,6 +1348,12 @@ class GDataFileSystem : public GDataFileSystemInterface,
   int num_pending_tasks_;
   base::Lock num_pending_tasks_lock_;
 
+  // Number of active update requests.
+  int num_update_requests_;
+
+  // Periodic timer for checking updates.
+  base::Timer update_timer_;
+
   // True if hosted documents should be hidden.
   bool hide_hosted_docs_;