Add an experimental standalone content suggestions UI.

chrome/android/java/res/menu/main_menu.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. -->
 
 <menu xmlns:android="http://schemas.android.com/apk/res/android">
     <!-- These menu items are common to tablet and phone. -->
     <group android:id="@+id/PAGE_MENU"
         android:visible="false">
         <item android:id="@+id/icon_row_menu_id"
@@ skipping 52 matching lines @@
             android:icon="?android:attr/listChoiceIndicatorMultiple" />
         <item android:id="@+id/reader_mode_prefs_id"
             android:title="@string/menu_reader_mode_prefs"
             android:icon="@drawable/reader_mode_prefs_icon" />
         <item android:id="@+id/preferences_id"
             android:title="@string/menu_preferences" />
         <item android:id="@+id/help_id"
             android:title="@string/menu_help" />
         <item android:id="@+id/enter_vr_id"
             android:title="@string/enter_vr" />
+        <item android:id="@+id/content_suggestions_standalone_ui"
+            android:title="@string/content_suggestions_standalone_ui" />
     </group>
 
     <!-- Items shown only in the tab switcher -->
     <group android:id="@+id/OVERVIEW_MODE_MENU"
         android:visible="false">
          <item android:id="@id/new_tab_menu_id"
              android:title="@string/menu_new_tab" />
          <item android:id="@id/new_incognito_tab_menu_id"
              android:title="@string/menu_new_incognito_tab" />
          <item android:id="@+id/close_all_tabs_menu_id"
              android:title="@string/menu_close_all_tabs" />
          <item android:id="@+id/close_all_incognito_tabs_menu_id"
              android:title="@string/menu_close_all_incognito_tabs" />
          <item android:id="@id/preferences_id"
              android:title="@string/menu_preferences" />
     </group>
 
     <!-- Items shown only when the tablet has no visible tabs -->
     <group android:id="@+id/TABLET_EMPTY_MODE_MENU"
         android:visible="false">
         <item android:id="@id/new_tab_menu_id"
             android:title="@string/menu_new_tab" />
         <item android:id="@id/new_incognito_tab_menu_id"
             android:title="@string/menu_new_incognito_tab" />
         <item android:id="@id/preferences_id"
             android:title="@string/menu_preferences" />
     </group>
 </menu>