Added implementation of SyncEventObserver to route events to Javascript Extension.

chrome/browser/extensions/event_names.cc

Index: chrome/browser/extensions/event_names.cc
diff --git a/chrome/browser/extensions/event_names.cc b/chrome/browser/extensions/event_names.cc
index 93aa3ea1b85486f62bb7b47bf59b494f95be084c..97ce857833482798cf0706b4f3242abde83f866e 100644
--- a/chrome/browser/extensions/event_names.cc
+++ b/chrome/browser/extensions/event_names.cc
@@ -76,6 +76,8 @@ const char kOnStorageAvailableCapacityChanged[] =
 const char kOnStorageAdded[] = "experimental.systemInfo.storage.onAdded";
 const char kOnStorageRemoved[] = "experimental.systemInfo.storage.onRemoved";
 
+const char kOnSyncStateChanged[] = "syncFileSystem.onSyncStateChanged";
+
 }  // namespace event_names
 
 }  // namespace extensions