PolymerTest.clearBody: don't remove vulcanized styles

chrome/test/data/webui/polymer_browser_test_base.js

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /**
  * @fileoverview Framework for running JavaScript tests of Polymer elements.
  */
 
 /**
  * Test fixture for Polymer element testing.
@@ skipping 170 matching lines @@
   var promise = new Promise(function(resolve, reject) {
     script.onload = resolve;
     script.onerror = reject;
   });
   script.src = src;
   document.head.appendChild(script);
   return promise;
 };
 
 /**
- * Removes all content from the body.
+ * Removes all content from the body, save for the global <style> elements
+ * used by a vulcanized build.
  */
 PolymerTest.clearBody = function() {
-  document.body.innerHTML = '';
+  var vulcanizeDiv = document.querySelector('body > div[hidden][by-vulcanize]');

[dpapad, 2017/04/24 18:35:15]

Would it be simpler to do the following?

var toRemove = document.body.querySelectorAll('[hidden][by-vulcanize]
:not(style)');
// iterate toRemove and call remove()

[dpapad, 2017/04/25 01:11:09]

Or maybe even better to use the following selector: '[hidden][by-vulcanize] >
:not(style)'

+  document.body.innerHTML='';
+  if (!vulcanizeDiv)
+    return;
+
+  if (!vulcanizeDiv.hasAttribute('processed-by-test')) {

[dpapad, 2017/04/24 18:35:15]

What is "processed-by-test"?

+    for (var child of vulcanizeDiv.children) {
+      if (child.tagName != 'STYLE')
+        child.remove();
+    }
+    vulcanizeDiv.setAttribute('processed-by-test', '');
+  }
+
+  document.body.appendChild(vulcanizeDiv);
 };
 
 /**
  * Helper function to return the list of extra libraries relative to basePath.
  */
 PolymerTest.getLibraries = function(basePath) {
   // Ensure basePath ends in '/'.
   if (basePath.length && basePath[basePath.length - 1] != '/')
     basePath += '/';
 
   return PolymerTest.prototype.extraLibraries.map(function(library) {
     return basePath + library;
   });
 };
 
 /*
  * Waits for queued up tasks to finish before proceeding. Inspired by:
  * https://github.com/Polymer/web-component-tester/blob/master/browser/environment/helpers.js#L97
  */
 PolymerTest.flushTasks = function() {
   Polymer.dom.flush();
   // Promises have microtask timing, so we use setTimeout to explicity force a
   // new task.
   return new Promise(function(resolve, reject) {
     window.setTimeout(resolve, 0);
   });
 };