DevTools: Use object spread operator in AxeCoreTestRunner.js

Support for ES9 features like object spread was enabled in https://crrev.com/d2af1fc

Change-Id: I938768072adc451d006f6f7d374bd7148a3bf084
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1689002Reviewed-by: Erik Luo <luoe@chromium.org>
Commit-Queue: John Emau <johnemau@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#676239}

third_party/blink/renderer/devtools/front_end/axe_core_test_runner/AxeCoreTestRunner.js

@@ -104,10 +104,10 @@ AxeCoreTestRunner.processAxeResultNodesArray = function(nodes) {
 };
 
 AxeCoreTestRunner.runValidation = async function(element, rules, config) {
-  axe.configure(Object.assign({}, DEFAULT_CONFIG, config));
+  axe.configure({...DEFAULT_CONFIG, ...config});
 
   try {
-    const results = await axe.run(element, {rules: Object.assign({}, DISABLED_RULES, rules)});
+    const results = await axe.run(element, {rules: {...DISABLED_RULES, ...rules}});
     const violations = AxeCoreTestRunner.processAxeResult(results.violations);
     TestRunner.addResult(`aXe violations: ${violations}\n`);
   } catch (e) {