Adds a webstorePrivate method for silently installing extensions.

chrome/test/data/extensions/api_test/webstore_private/common.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.
 
 // The id of an extension we're using for install tests.
 var extensionId = "enfkhcelefdadlmkffamgdlgplcionje";
 
 // The id of an app we're using for install tests.
 var appId = "iladmdjkfniedhfhcfoefgojhgaiaccc";
 
 var assertEq = chrome.test.assertEq;
 var assertNoLastError = chrome.test.assertNoLastError;
+var assertTrue = chrome.test.assertTrue;
 var callbackFail = chrome.test.callbackFail;
 var callbackPass = chrome.test.callbackPass;
 var listenOnce = chrome.test.listenOnce;
 var runTests = chrome.test.runTests;
 var succeed = chrome.test.succeed;
 
 // Calls |callback| with true/false indicating whether an item with an id of
 // extensionId is installed.
 function checkInstalled(callback) {
   chrome.management.getAll(function(extensions) {
@@ skipping 36 matching lines @@
     return cachedManifest;
 
   // Do a synchronous XHR to get the manifest.
   var xhr = new XMLHttpRequest();
   xhr.open("GET",
            alternativePath ? alternativePath : "extension/manifest.json",
            false);
   xhr.send(null);
   return xhr.responseText;
 }