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..12a87c0f687e91178d9e29f58a98f19f7308f7be 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 +176,10 @@ class GDataFileSystemInterface {
   virtual void AddObserver(Observer* observer) = 0;
   virtual void RemoveObserver(Observer* observer) = 0;
 
+  // Starts and stops periodic updates.
+  virtual void StartUpdates() = 0;

[satorux1, 2012/05/03 18:46:20]

Please also explain a bit more about these functions. For instance,
StartUpdates() will start periodic updates only if it's not yet started, right? 

Likewise, StopUpdates() stops it only if the number of update requests becomes
zero, right?

that said, RequestStartPeriodicUpdates(), RequestStopPeriodicUpdates() may be
better names.

[hshi, 2012/05/03 19:09:19]

Done. Although I think "Periodic" may be redundant.

[satorux1, 2012/05/03 19:18:36]

Agreed.

+  virtual void StopUpdates() = 0;
+
   // Enum defining origin of a cached file.
   enum CachedFileOrigin {
     CACHED_FILE_FROM_SERVER = 0,
@@ -400,6 +405,8 @@ class GDataFileSystem : public GDataFileSystemInterface,
   virtual void Initialize() OVERRIDE;
   virtual void AddObserver(Observer* observer) OVERRIDE;
   virtual void RemoveObserver(Observer* observer) OVERRIDE;
+  virtual void StartUpdates() OVERRIDE;
+  virtual void StopUpdates() OVERRIDE;
   virtual void Authenticate(const AuthStatusCallback& callback) OVERRIDE;
   virtual void FindEntryByResourceIdSync(const std::string& resource_id,
                                          FindEntryDelegate* delegate) OVERRIDE;
@@ -1303,6 +1310,9 @@ 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 +1343,12 @@ 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::RepeatingTimer<GDataFileSystem> update_timer_;
+
   // True if hosted documents should be hidden.
   bool hide_hosted_docs_;