[Android] Updating menu assets.

chrome/android/shell/res/menu/main_menu.xml

 <?xml version="1.0" encoding="utf-8"?>
 <!-- Copyright 2013 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" >
 
     <group
         android:id="@+id/MAIN_MENU"
         android:visible="false" >
         <item>
             <menu>
                 <item
                     android:id="@+id/back_menu_id"
-                    android:icon="@drawable/back_button_selector"
+                    android:icon="@drawable/btn_back"
                     android:title="@string/accessibility_menu_back"/>
                 <item
                     android:id="@+id/forward_menu_id"
-                    android:icon="@drawable/forward_button_selector"
+                    android:icon="@drawable/btn_forward"
                     android:title="@string/accessibility_menu_forward"/>
                 <item
                     android:id="@+id/bookmark_this_page_id"
-                    android:icon="@drawable/star"
+                    android:icon="@drawable/btn_star"
                     android:title="@string/accessibility_menu_bookmark"/>
             </menu>
         </item>
         <item
             android:id="@+id/signin"
             android:title="@string/signin_sign_in"/>
         <item
             android:id="@+id/print"
             android:title="@string/print_menu"/>
         <item
             android:id="@+id/distill_page"
             android:title="@string/distill_page_menu"/>
         <item>
             <menu>
                 <item
                     android:id="@+id/share_menu_id"
                     android:title="@string/menu_share_page"/>
                 <item
                     android:id="@+id/direct_share_menu_id"
                     android:title="@null"/>
             </menu>
         </item>
     </group>
 
 </menu>