Change the first parameter of savePage.saveAsMHTML to be a dictionary.

chrome/test/data/extensions/api_test/save_page/test.js

 // Copyright (c) 2011 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.
 
 // API test for chrome.extension.savePage.
 // browser_tests.exe --gtest_filter=ExtensionApiTest.SavePage
 
 const assertEq = chrome.test.assertEq;
 const assertTrue = chrome.test.assertTrue;
 
@@ skipping 11 matching lines @@
 }
 
 chrome.test.getConfig(function(config) {
   testUrl = testUrl.replace(/PORT/, config.testServer.port);
 
   chrome.test.runTests([
     function savePageAsMHTML() {
       chrome.tabs.getSelected(null, function(tab) {
         chrome.tabs.update(null, { "url": testUrl });
         waitForCurrentTabLoaded(function() {
-          chrome.experimental.savePage.saveAsMHTML(tab.id, function(data) {
+          chrome.experimental.savePage.saveAsMHTML({ "tabId": tab.id },
+              function(data) {
             assertEq(undefined, chrome.extension.lastError);
             assertTrue(data != null);
             // It should contain few KBs of data.
             assertTrue(data.size > 100);
             // Let's make sure it contains some well known strings.
             var reader = new FileReader();
             reader.onload = function(e) {
               var text = e.target.result;
               assertTrue(text.indexOf(testUrl) != -1);
               assertTrue(text.indexOf("logo.png") != -1);
               chrome.test.notifyPass();
             };
             reader.readAsText(data);
           });
         });
       });
     }
   ]);
 });