Fix MaterialPDFExtensionTest.ElementsTest in Polymer 1.0.5

chrome/test/data/pdf/material_elements_test.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.
 
 /**
  * Standalone unit tests of the PDF Polymer elements.
  */
 var tests = [
   /**
    * Test that viewer-page-selector reacts correctly to text entry. The page
@@ skipping 117 matching lines @@
 
       var subBookmarkDiv =
           rootBookmark.shadowRoot.querySelector('.sub-bookmark');
 
       chrome.test.assertTrue(subBookmarkDiv.hidden);
       MockInteractions.tap(rootBookmark.$.expand);
       chrome.test.assertFalse(subBookmarkDiv.hidden);
       chrome.test.assertEq('hidden', subBookmarks[1].$.expand.style.visibility);
 
       chrome.test.succeed();
-    });
+    }, 10);

[raymes, 2015/07/30 04:33:22]

Hmm doing this could make the test flaky. If there is no polymer event that we
could catch which signals the bookmarks have loaded, could we fire an event
ourselves from inside the last bookmark to load?

[tsergeant, 2015/07/30 05:02:09]

My understanding of it (based on reading the Polymer.Async code) is that tasks
queued with a delay value cannot preempt tasks without a delay value. Tasks with
a delay are scheduled on the browser message loop using setTimeout, and Polymer
doesn't relinquish control back to that message loop until all non-delay tasks
are completed. All other tasks fired during this test have no delay, so this
task will be called last.

I don't think the test should be flaky for that reason. Otherwise, adding a
second nested .async() call also appears to fix the issue.

[tsergeant, 2015/07/30 07:04:05]

Actually, I've now convinced myself the other way. It was possible for control
to go back to the browser, depending on exactly how tasks are queued. Reading a
bunch *more* Polymer code, it seems that `Polymer.dom.flush()` is the best way
to force all templates to render (see [1]). With this, the test passes with no
async tasks at all.

[1]
https://github.com/Polymer/polymer/commit/89a767c1f97bff9d96f063f4ecfee79bc2f...

   }
 ];
 
 importTestHelpers().then(function() {
   chrome.test.runTests(tests);
 });