drive: Introduce DriveSystemServiceObserver

chrome/browser/chromeos/drive/drive_system_service.h

Index: chrome/browser/chromeos/drive/drive_system_service.h
diff --git a/chrome/browser/chromeos/drive/drive_system_service.h b/chrome/browser/chromeos/drive/drive_system_service.h
index 7e63a12915ce50769a031c47023d13dceb354827..cb130441643fcac1a550363da81770352806f01f 100644
--- a/chrome/browser/chromeos/drive/drive_system_service.h
+++ b/chrome/browser/chromeos/drive/drive_system_service.h
@@ -11,6 +11,7 @@
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/singleton.h"
 #include "base/memory/weak_ptr.h"
+#include "base/observer_list.h"
 #include "base/threading/sequenced_worker_pool.h"
 #include "chrome/browser/chromeos/drive/drive_file_error.h"
 #include "chrome/browser/chromeos/drive/drive_file_system_util.h"
@@ -40,6 +41,22 @@ class EventLogger;
 class FileWriteHelper;
 class StaleCacheFilesRemover;
 
+// Interface for classes that need to observe events from DriveSystemService.
+// All events are notified on UI thread.
+class DriveSystemServiceObserver {
+ public:
+  // Triggered when the file system is mounted.
+  virtual void OnFileSystemMounted() {
+  }
+
+  // Triggered when the file system is being unmounted.
+  virtual void OnFileSystemBeingUnmounted() {
+  }
+
+ protected:
+  virtual ~DriveSystemServiceObserver() {}
+};
+
 // DriveSystemService runs the Drive system, including the Drive file system
 // implementation for the file manager, and some other sub systems.
 //
@@ -65,6 +82,10 @@ class DriveSystemService : public ProfileKeyedService,
   // ProfileKeyedService override:
   virtual void Shutdown() OVERRIDE;
 
+  // Adds and removes the observer.
+  void AddObserver(DriveSystemServiceObserver* observer);
+  void RemoveObserver(DriveSystemServiceObserver* observer);
+
   google_apis::DriveServiceInterface* drive_service() {
     return drive_service_.get();
   }
@@ -152,6 +173,8 @@ class DriveSystemService : public ProfileKeyedService,
   scoped_ptr<StaleCacheFilesRemover> stale_cache_files_remover_;
   scoped_refptr<DriveFileSystemProxy> file_system_proxy_;
 
+  ObserverList<DriveSystemServiceObserver> observers_;
+
   // Note: This should remain the last member so it'll be destroyed and
   // invalidate its weak pointers before any other members are destroyed.
   base::WeakPtrFactory<DriveSystemService> weak_ptr_factory_;