Update perf test for CE def style to use CSSStyleSheet constructor

Constructor for CSSStyleSheets has changed in a recent CL, so this test
is failing.

TBR=crouleau@chromium.org

Bug: 914084
Change-Id: Icbf34425f9141bdd581a0c2ab9b568aaf058a358
Reviewed-on: https://chromium-review.googlesource.com/c/1373373Reviewed-by: Rakina Zata Amni <rakina@chromium.org>
Reviewed-by: Kent Tamura <tkent@chromium.org>
Commit-Queue: Rakina Zata Amni <rakina@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615843}

third_party/blink/perf_tests/dom/custom-element-default-style.html

@@ -5,7 +5,7 @@
 <script>
 const holderElement = document.getElementById("holder");
 
-const constructedStyleSheet = document.createEmptyCSSStyleSheet();
+const constructedStyleSheet = new CSSStyleSheet();
 constructedStyleSheet.insertRule("* { color: red; }");
 window.customElements.define("element-constructed", class extends HTMLElement {
   constructor() {