Skip enhanced bookmarks cluster requests if it's not being used.

components/enhanced_bookmarks/bookmark_server_service.cc

Index: components/enhanced_bookmarks/bookmark_server_service.cc
diff --git a/components/enhanced_bookmarks/bookmark_server_service.cc b/components/enhanced_bookmarks/bookmark_server_service.cc
index 1e6f4b0f102b0da8db7cd5c8de378678a2b0dcf3..366f2a963fd33f7e50db15f8ee66b095c3d3b796 100644
--- a/components/enhanced_bookmarks/bookmark_server_service.cc
+++ b/components/enhanced_bookmarks/bookmark_server_service.cc
@@ -46,6 +46,10 @@ void BookmarkServerService::RemoveObserver(
   observers_.RemoveObserver(observer);
 }
 
+bool BookmarkServerService::MightHaveObservers() {
+  return observers_.might_have_observers();
+}
+
 const BookmarkNode* BookmarkServerService::BookmarkForRemoteId(
     const std::string& remote_id) const {
   return model_->BookmarkForRemoteId(remote_id);