Split the private webstore install API into two parts....

chrome/test/data/extensions/api_test/extension_gallery_install/common.js

+// Copyright (c) 2010 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 extension_id = "ldnnhddmnhbkjipkidpdiheffobcpfmf";
+
+var assertEq = chrome.test.assertEq;
+var assertNoLastError = chrome.test.assertNoLastError;
+var succeed = chrome.test.succeed;
+
+function checkInstalled(callback) {
+  chrome.management.getAll(function(extensions) {
+    var found = false;
+    extensions.forEach(function(extension) {

[Erik does not do reviews, 2010/11/10 16:47:45]

you can use one of the more recent built-in array functions for this:
callback(extensions.some(function(ext) { return extension_id == ext.id); });

[asargent_no_longer_on_chrome, 2010/11/10 22:58:23]

nice - I hadn't heard of that one before. done.

+      if (extension_id == extension.id)
+        found = true;
+    });
+
+    callback(found);
+  });
+}