Reduce the memory usage of bookmarks storage

components/sync_bookmarks/bookmark_change_processor.cc

Index: components/sync_bookmarks/bookmark_change_processor.cc
diff --git a/components/sync_bookmarks/bookmark_change_processor.cc b/components/sync_bookmarks/bookmark_change_processor.cc
index 96d50b12215ba35fa52175d51c3ad4c06b168a5c..63930d1d69058581c8e83a302b015749ac44d4d5 100644
--- a/components/sync_bookmarks/bookmark_change_processor.cc
+++ b/components/sync_bookmarks/bookmark_change_processor.cc
@@ -968,7 +968,9 @@ void BookmarkChangeProcessor::SetSyncNodeFavicon(
         sync_node->GetBookmarkSpecifics());
     updated_specifics.set_favicon(favicon_bytes->front(),
                                   favicon_bytes->size());
-    updated_specifics.set_icon_url(bookmark_node->icon_url().spec());
+    updated_specifics.set_icon_url(bookmark_node->icon_url()
+                                       ? bookmark_node->icon_url()->spec()
+                                       : std::string());
     sync_node->SetBookmarkSpecifics(updated_specifics);
   }
 }