Implement "streaming" $i18n{} replacer

content/browser/webui/web_ui_data_source_impl.cc

Index: content/browser/webui/web_ui_data_source_impl.cc
diff --git a/content/browser/webui/web_ui_data_source_impl.cc b/content/browser/webui/web_ui_data_source_impl.cc
index 0b07bddf0043f85ecc50e78ef55699b85ba00dae..86469a5503b5d9b786bf66a80afaa24bdb347252 100644
--- a/content/browser/webui/web_ui_data_source_impl.cc
+++ b/content/browser/webui/web_ui_data_source_impl.cc
@@ -189,6 +189,10 @@ void WebUIDataSourceImpl::DisableI18nAndUseGzipForAllPaths() {
   use_gzip_for_all_paths_ = true;
 }
 
+const ui::TemplateReplacements* WebUIDataSourceImpl::GetTemplateReplacements() const {
+  return replacements_.empty() ? nullptr : &replacements_;
+}
+
 std::string WebUIDataSourceImpl::GetSource() const {
   return source_name_;
 }