Handle both plural and singular tab switcher content descriptions.

chrome/android/java/res/layout-sw600dp/toolbar.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 toolbar containing the URL bar, back button, and NTP button.
 -->
 
 <org.chromium.chrome.browser.toolbar.ToolbarTablet
     xmlns:android="http://schemas.android.com/apk/res/android"
@@ skipping 41 matching lines @@
             android:layout_marginTop="5dp"
             android:layout_weight="1"
             android:layout_gravity="top|center"
             android:background="@drawable/textbox"
             android:paddingEnd="1dp"
             android:paddingStart="2dp" />
 
         <ImageButton
             android:id="@+id/tab_switcher_button"
             style="@style/ToolbarButton"
-            android:contentDescription="@string/accessibility_toolbar_btn_tabswitcher_toggle"
+            android:contentDescription="@string/accessibility_toolbar_btn_tabswitcher_toggle_default"
             android:visibility="gone" />
 
         <FrameLayout
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:id="@+id/menu_button_wrapper" >
 
             <org.chromium.chrome.browser.widget.TintedImageButton
                 android:id="@+id/menu_button"
                 style="@style/ToolbarMenuButtonTablet"
                 android:src="@drawable/btn_menu"
                 android:contentDescription="@string/accessibility_toolbar_btn_menu" />
 
             <ImageView
                 android:id="@+id/menu_badge"
                 style="@style/ToolbarMenuButtonTablet"
                 android:src="@drawable/badge_update_dark"
                 android:contentDescription="@null"
                 android:importantForAccessibility="no"
                 android:visibility="invisible" />
 
         </FrameLayout>
     </LinearLayout>
 </org.chromium.chrome.browser.toolbar.ToolbarTablet>