Add `privacy.network.webRTCMultipleRoutesEnabled` to extensions API.

chrome/test/data/extensions/api_test/preference/standard/test.js

 // Copyright (c) 2012 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.
 
 // Preferences API test
 // Run with browser_tests --gtest_filter=ExtensionApiTest.PreferenceApi
 
 var preferences_to_test = [
   {
     root: chrome.privacy.network,
     preferences: [
-      'networkPredictionEnabled'
+      'networkPredictionEnabled',
+      'webRTCMultipleRoutesEnabled'
     ]
   },
   {
     root: chrome.privacy.websites,
     preferences: [
       'thirdPartyCookiesAllowed',
       'hyperlinkAuditingEnabled',
       'referrersEnabled',
       'protectedContentEnabled'
     ]
   },
   {
     root: chrome.privacy.services,
     preferences: [
       'alternateErrorPagesEnabled',
       'autofillEnabled',
       'hotwordSearchEnabled',
       'passwordSavingEnabled',
       'safeBrowsingEnabled',
       'safeBrowsingExtendedReportingEnabled',
       'searchSuggestEnabled',
       'spellingServiceEnabled',
       'translationServiceEnabled'
     ]
   },
 ];
 
+// Some preferences are only present on certain platforms or are hidden
+// behind flags and might not be present when this test runs.
+var possibly_missing_preferences = new Set([
+  'protectedContentEnabled',    // Windows/ChromeOS only
+  'webRTCMultipleRoutesEnabled' // requires ENABLE_WEBRTC=1
+]);
+
 function expect(expected, message) {
   return chrome.test.callbackPass(function(value) {
     chrome.test.assertEq(expected, value, message);
   });
 }
 
 function expectFalse(pref) {
   return expect({
     value: false,
     levelOfControl: 'controllable_by_this_extension'
   }, '`' + pref + '` is expected to be false.');
 }
 
 function prefGetter(pref) {
-  if (pref === 'protectedContentEnabled' && !this[pref]) {
-    // `protectedContentEnabled` is Windows/ChromeOS only, so it might not exist
-    // when this test runs, and that's pretty much OK.
+  if (possibly_missing_preferences.has(pref) && !this[pref]) {
     return true;
   }
   this[pref].get({}, expectFalse(pref));
 }
 
 function prefSetter(pref) {
-  if (pref === 'protectedContentEnabled' && !this[pref]) {
-    // `protectedContentEnabled` is Windows/ChromeOS only, so it might not exist
-    // when this test runs, and that's pretty much OK.
+  if (possibly_missing_preferences.has(pref) && !this[pref]) {
     return true;
   }
   this[pref].set({value: true}, chrome.test.callbackPass());
 }
 
 chrome.test.runTests([
   function getPreferences() {
     for (var i = 0; i < preferences_to_test.length; i++) {
       preferences_to_test[i].preferences.forEach(
           prefGetter.bind(preferences_to_test[i].root));
     }
   },
   function setGlobals() {
     for (var i = 0; i < preferences_to_test.length; i++) {
       preferences_to_test[i].preferences.forEach(
           prefSetter.bind(preferences_to_test[i].root));
     }
   }
 ]);