Modify pdf_scripting_api.js to support postMessage using BrowserPlugin

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.
 
+var scriptingAPI;
+
 /**
  * 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.setZoom(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) {
+    scriptingAPI.getAccessibilityJSON(chrome.test.callbackPass(function(json) {
       var dict = JSON.parse(json);
       chrome.test.assertEq(true, dict.copyable);
       chrome.test.assertEq(true, dict.loaded);
       chrome.test.assertEq(1, dict.numberOfPages);
     }));
   },
 
   function testAccessibilityWithPage() {
-    var client = new PDFScriptingAPI(window, window.location.origin);
-    client.setDestinationWindow(window);
-    client.getAccessibilityJSON(chrome.test.callbackPass(function(json) {
+    scriptingAPI.getAccessibilityJSON(chrome.test.callbackPass(function(json) {
       var dict = JSON.parse(json);
       chrome.test.assertEq(612, dict.width);
       chrome.test.assertEq(792, dict.height);
       chrome.test.assertEq(1.0, dict.textBox[0].fontSize);
       chrome.test.assertEq('text', dict.textBox[0].textNodes[0].type);
       chrome.test.assertEq('this is some text',
                            dict.textBox[0].textNodes[0].text);
       chrome.test.assertEq(1.0, dict.textBox[1].fontSize);
       chrome.test.assertEq('text', dict.textBox[1].textNodes[0].type);
       chrome.test.assertEq('some more text',
                            dict.textBox[1].textNodes[0].text);
     }), 0);
   }
 ];
 
-if (viewer.loaded) {
+var scriptingAPI = new PDFScriptingAPI(window, window);
+scriptingAPI.setLoadCallback(function() {
   chrome.test.runTests(tests);
-} else {
-  window.addEventListener('pdfload', function() {
-    chrome.test.runTests(tests);
-  });
-}
+});