Media Galleries API Scanning: Add Scan Permission and basic test.

chrome/test/data/extensions/api_test/media_galleries/scan/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 mediaGalleries = chrome.mediaGalleries;
+
+function StartAndCancelMediaScanTest() {
+  function StartMediaScanTest() {
+    var startEventListener = function(details) {
+      chrome.test.assertEq('start', details.type);
+      mediaGalleries.onScanProgress.removeListener(startEventListener);
+      CancelMediaScanTest();
+    }
+    mediaGalleries.onScanProgress.addListener(startEventListener);
+
+    mediaGalleries.startMediaScan();
+  }
+
+  function CancelMediaScanTest() {
+    var cancelEventListener = function(details) {
+      chrome.test.assertEq('cancel', details.type);
+      mediaGalleries.onScanProgress.removeListener(cancelEventListener);
+      chrome.test.succeed();
+    };
+    mediaGalleries.onScanProgress.addListener(cancelEventListener);
+
+    mediaGalleries.cancelMediaScan();
+  }
+
+  StartMediaScanTest();
+}
+
+CreateDummyWindowToPreventSleep();
+
+chrome.test.runTests([
+  StartAndCancelMediaScanTest,
+]);