Video Player: Check Cast extension before launching cast feature

ui/file_manager/video_player/js/cast/cast_extension_discoverer.js

Index: ui/file_manager/video_player/js/cast/cast_extension_discoverer.js
diff --git a/ui/file_manager/video_player/js/cast/cast_extension_discoverer.js b/ui/file_manager/video_player/js/cast/cast_extension_discoverer.js
new file mode 100644
index 0000000000000000000000000000000000000000..e980e4ae2df0d22485f33ab53335b908e756e128
--- /dev/null
+++ b/ui/file_manager/video_player/js/cast/cast_extension_discoverer.js
@@ -0,0 +1,83 @@
+// 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.
+
+'use strict';
+
+/**
+ * Discover the ID of installed cast extesnion.
+ * @constructor
+ */
+function CastExtensionDiscoverer() {
+}
+
+/**
+ * Tentatice IDs to try.
+ * @type {Array.<string>}
+ * @const
+ */
+CastExtensionDiscoverer.CAST_EXTENSION_IDS = [
+  'boadgeojelhgndaghljhdicfkmllpafd', // release
+  'dliochdbjfkdbacpmhlcpmleaejidimm', // beta
+  'hfaagokkkhdbgiakmmlclaapfelnkoah',
+  'fmfcbgogabcbclcofgocippekhfcmgfj',
+  'enhhojjnijigcajfphajepfemndkmdlo'
+];
+
+/**
+ * @param {function(string)} callback Callback called with the extension ID. The
+ *     ID may be null if extension is not found.
+ */
+CastExtensionDiscoverer.findInstalledExtension = function(callback) {
+  CastExtensionDiscoverer.findInstalledExtensionHelper_(0, callback);
+};
+
+/**
+ * @param {number} index Current index which is tried to check.
+ * @param {function(string)} callback Callback function which will be called
+ *     the extension is found.
+ * @private
+ */
+CastExtensionDiscoverer.findInstalledExtensionHelper_ = function(index,
+    callback) {
+  if (index === CastExtensionDiscoverer.CAST_EXTENSION_IDS.length) {
+    // no extension found.
+    callback(null);
+    return;
+  }
+
+  CastExtensionDiscoverer.isExtensionInstalled_(
+      CastExtensionDiscoverer.CAST_EXTENSION_IDS[index],
+      function(installed) {
+        if (installed) {
+          callback(CastExtensionDiscoverer.CAST_EXTENSION_IDS[index]);
+        } else {
+          CastExtensionDiscoverer.findInstalledExtensionHelper_(index + 1,
+                                                                callback);
+        }
+      });
+};
+
+/**
+ * The result will be notified on |callback|. True if installed, false not.
+ * @param {string} extensionId Id to be checked.
+ * @param {function(boolean)} callback Callback to notify the result.
+ * @private
+ */
+CastExtensionDiscoverer.isExtensionInstalled_ =
+    function(extensionId, callback) {
+
+  var xhr = new XMLHttpRequest();
+  var url = 'chrome-extension://' + extensionId + '/cast_sender.js';
+  xhr.open('GET', url, true);
+  xhr.onerror = function() { callback(false); };
+  xhr.onreadystatechange =
+      /** @param {*} response */
+      function(event) {
+        if (xhr.readyState == 4 && xhr.status === 200) {
+          // Cast extension found.
+          callback(true);
+        }
+      }.wrap(this);
+  xhr.send();
+};