Use native CSS variables in Polymer

ui/webui/resources/js/polymer_config.js

Index: ui/webui/resources/js/polymer_config.js
diff --git a/ui/webui/resources/js/polymer_config.js b/ui/webui/resources/js/polymer_config.js
index 8e95ec972942297dcac1a4b3812fed991be27904..02e4d9f305bf5b184ca1a0db4d0d07cd0fa6081d 100644
--- a/ui/webui/resources/js/polymer_config.js
+++ b/ui/webui/resources/js/polymer_config.js
@@ -2,7 +2,12 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-if (typeof Polymer == 'undefined')
-  Polymer = {dom: 'shadow', lazyRegister: true};
-else
+if (typeof Polymer == 'undefined') {
+  Polymer = {
+    dom: 'shadow',
+    lazyRegister: true,
+    useNativeCSSProperties: true,
+  };
+} else {
   console.error('Polymer is already defined.');
+}