Improve scrolling performance in OOP PDF

chrome/test/data/pdf/basic_plugin_test.js

 // Copyright 2014 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.
 
 /**
  * These tests require that the PDF plugin be available to run correctly.
  */
 var tests = [
   /**
    * Test that the page is sized to the size of the document.
    */
   function testPageSize() {
     // Verify that the initial zoom is less than or equal to 100%.
     chrome.test.assertTrue(viewer.viewport.zoom <= 1);
 
-    viewer.viewport.zoom = 1;
+    viewer.viewport.setZoomForTest_(1);
     var sizer = document.getElementById('sizer');
     chrome.test.assertEq(826, sizer.offsetWidth);
     chrome.test.assertEq(1066, sizer.offsetHeight);
     chrome.test.succeed();
   },
 
   function testAccessibility() {
     var client = new PDFScriptingAPI(window, window.location.origin);
     client.setDestinationWindow(window);
     client.getAccessibilityJSON(chrome.test.callbackPass(function(json) {
@@ skipping 23 matching lines @@
   }
 ];
 
 if (viewer.loaded) {
   chrome.test.runTests(tests);
 } else {
   window.addEventListener('pdfload', function() {
     chrome.test.runTests(tests);
   });
 }