Disable document mode.

chrome/android/java/res/xml/main_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. -->
 
 <PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
 
     <org.chromium.chrome.browser.preferences.SignInPreference
         android:key="sign_in"
         android:title="@string/sign_in_to_chrome" />
 
     <PreferenceCategory
         android:title="@string/prefs_section_basics"/>
     <org.chromium.chrome.browser.preferences.SearchEnginePreference
         android:key="search_engine"
         android:title="@string/prefs_search_engine"/>
-    <Preference
-        android:fragment="org.chromium.chrome.browser.preferences.DocumentModePreference"
-        android:key="document_mode"
-        android:title="@string/tabs_and_apps_title" />
     <org.chromium.chrome.browser.preferences.ChromeBasePreference
         android:fragment="org.chromium.chrome.browser.preferences.autofill.AutofillPreferences"
         android:key="autofill_settings"
         android:title="@string/prefs_autofill" />
     <org.chromium.chrome.browser.preferences.ChromeBasePreference
         android:fragment="org.chromium.chrome.browser.preferences.password.SavePasswordsPreferences"
         android:key="saved_passwords"
         android:title="@string/prefs_saved_passwords" />
     <Preference
         android:fragment="org.chromium.chrome.browser.preferences.HomepagePreferences"
@@ skipping 17 matching lines @@
     <org.chromium.chrome.browser.preferences.ChromeBasePreference
         android:fragment="org.chromium.chrome.browser.preferences.datareduction.DataReductionPreferences"
         android:key="data_reduction"
         android:title="@string/data_reduction_title" />
     <Preference
         android:fragment="org.chromium.chrome.browser.preferences.AboutChromePreferences"
         android:key="about_chrome"
         android:title="@string/prefs_about_chrome" />
 
 </PreferenceScreen>