Added implementation of SyncEventObserver to route events to Javascript Extension.

chrome/common/extensions/api/sync_file_system.idl

 // Copyright (c) 2012 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.
 
 namespace syncFileSystem {
   dictionary StorageInfo {
     long usage_bytes;
     long quota_bytes;
   };
   
   dictionary SyncState {
     DOMString service_name;  // i.e. ‘drive’
     SyncStateStatus state;
     DOMString description;
   };
   
+  enum SyncOperationType {
+    added, updated, deleted
+  };
+  
   enum SyncStateStatus {
     // The sync service is being initialized (e.g. restoring data from the
     // database, checking connectivity and authenticating to the service etc).
-    INITIALIZING,
+    initializing,
 
     // The sync service is up and running.
-    RUNNING,
+    running,
 
     // The sync service is not synchronizing files because the remote service
     // needs to be authenticated by the user to proceed.
-    AUTHENTICATION_REQUIRED,
+    authentication_required,
 
     // The sync service is not synchronizing files because the remote service
     // is (temporarily) unavailable due to some recoverable errors, e.g.
     // network is offline, the remote service is down or not
     // reachable etc. More details should be given by |description| parameter
     // in OnSyncStateUpdated (which could contain service-specific details).
-    TEMPORARY_UNAVAILABLE,
+    temporary_unavailable,
 
     // The sync service is disabled and the content will never sync.
     // (E.g. this could happen when the user has no account on
     // the remote service or the sync service has had an unrecoverable
     // error.)
-    DISABLED
+    disabled
   };
 
   // [nodoc] A callback type for requestFileSystem.
   callback GetFileSystemCallback =
       void ([instanceOf=DOMFileSystem] object fileSystem);
       
   // [nodoc] A callback type for getUsageAndQuota.
   callback QuotaAndUsageCallback = void (StorageInfo info);
 
   // Returns true if operation was successful.  
@@ skipping 13 matching lines @@
     // Deletes everything in the syncable filesystem.
     static void deleteFileSystem([instanceOf=DOMFileSystem] object fileSystem,
                                   DeleteFileSystemCallback callback);
   };
   
   interface Events {
     // Fired when an error or other state change has happened in the
     // sync backend.  (E.g. the sync is temporarily disabled due to
     // network or authentication error etc)
     static void onSyncStateChanged(SyncState detail);
+    
+    // Fired when a file has been updated by the background sync service.
+    // TODO(calvinlo): Convert |file_entry_path| from to Webkit FileEntry.
+    static void onFileSynced(DOMString file_entry_path,
+                             SyncOperationType operation);
   };
 };