Fix MediaGalleriesPlatformAppBrowserTest tests with PlzNavigate.

chrome/test/data/extensions/api_test/media_galleries/common/common_injected.js

 // Copyright 2013 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.
 
 // Valid WEBP image.
 var validWEBPImageCase = {
   filename: "valid.webp",
   blobString: "RIFF0\0\0\0WEBPVP8 $\0\0\0\xB2\x02\0\x9D\x01\x2A" +
               "\x01\0\x01\0\x2F\x9D\xCE\xE7s\xA8((((\x01\x9CK(\0" +
               "\x05\xCE\xB3l\0\0\xFE\xD8\x80\0\0"
@@ skipping 206 matching lines @@
     reader.onerror = function(e) {
       chrome.test.fail("Unable to read test image: " + filename);
     };
 
     reader.readAsArrayBuffer(file);
   }
 
   parentDirectoryEntry.getFile(filename, {create: false}, verifyFileEntry,
                                chrome.test.fail);
 }
-
-// Create a dummy window to prevent the ProcessManager from suspending the
-// chrome-test app. Needed because the writer.onerror and writer.onwriteend
-// events do not qualify as pending callbacks, so the app looks dormant.
-function CreateDummyWindowToPreventSleep() {
-  chrome.app.runtime.onLaunched.addListener(function() {
-    chrome.app.window.create('dummy.html', {
-      outerBounds: {
-        width: 800,
-        height: 600,
-        left: 100,
-        top: 100,
-        minWidth: 800,
-        minHeight: 600
-      }
-    });
-  });
-}