Site Settings: Add Autoplay as a permission.

chrome/android/java/res/xml/site_settings_preferences.xml

 <?xml version="1.0" encoding="utf-8"?>
 <!-- Copyright 2015 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 list below All Sites is ordered by privacy-sensitive items first. If
      you are not sure where to add your item, add it above Storage. -->
 <PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
     <!-- All sites -->
     <Preference
@@ skipping 26 matching lines @@
         android:fragment="org.chromium.chrome.browser.preferences.website.SingleCategoryPreferences"
         android:key="popups" />
     <!-- Fullscreen -->
     <Preference
         android:fragment="org.chromium.chrome.browser.preferences.website.SingleCategoryPreferences"
         android:key="fullscreen" />
     <!-- Notifications -->
     <Preference
         android:fragment="org.chromium.chrome.browser.preferences.website.SingleCategoryPreferences"
         android:key="notifications" />
+    <!-- Autoplay -->
+    <Preference
+        android:fragment="org.chromium.chrome.browser.preferences.website.SingleCategoryPreferences"
+        android:key="autoplay" />
     <!-- Protected content -->
     <Preference
         android:fragment="org.chromium.chrome.browser.preferences.website.SingleCategoryPreferences"
         android:key="protected_content" />
     <!-- Background sync -->
     <Preference
         android:fragment="org.chromium.chrome.browser.preferences.website.SingleCategoryPreferences"
         android:key="background_sync" />
     <!-- Language -->
     <Preference
         android:fragment="org.chromium.chrome.browser.preferences.website.LanguagePreferences"
         android:key="language"
         android:title="@string/language"
         android:icon="@drawable/settings_language" />
     <!-- Storage -->
     <!-- TODO(finnur): Move this over to the new Usage screen, once it exists. -->
     <Preference
         android:fragment="org.chromium.chrome.browser.preferences.website.SingleCategoryPreferences"
         android:key="use_storage"
         android:title="@string/website_settings_storage"
         android:icon="@drawable/settings_storage" />
 </PreferenceScreen>