Fix test in shady DOM

test/unit/styling-scoped.html

@@ -751,7 +751,7 @@
       <style include="importing-double-shared-style double-shared-style"></style>
     </template>
     <script>
-    addEventListener('WebComponentsReady', () => {
+    HTMLImports.whenReady(() => {
       class DoubleSharedStylingElement extends Polymer.Element {
         static get is() { return 'double-shared-styling-element'; }
       }
@@ -1056,9 +1056,22 @@
     });
 
     test('only includes style modules once', function() {
-      assert.equal(el.shadowRoot.querySelector('style').textContent, `.double-shared-style {
+      const style = el.shadowRoot.querySelector('style');
+
+      // We cant use the regular "does a sub-node have the correct style",
+      // because we are actually need to assert on the actual style content.
+      // In native shadow dom, the style element resides in the shadowRoot,
+      // but in shadyDOM it has moved to the head and the selector has been altered.
+      if (style) {
+        assert.equal(style.textContent, `.double-shared-style {
   color: green;
 }`, 'There should be only one class selector in this style element');
+      } else {
+        assert.equal(document.head.querySelector('[scope="double-shared-styling-element"]').textContent,
+`.double-shared-style.double-shared-styling-element {
+  color: green;
+}`);
+      }
     });
   });