Animate hiding security button on custom tab toolbar

chrome/android/java/res/layout/custom_tabs_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. -->
 
 <org.chromium.chrome.browser.toolbar.CustomTabToolbar
     xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:chrome="http://schemas.android.com/apk/res-auto" >
     <org.chromium.chrome.browser.widget.TintedImageButton
         android:id="@+id/close_button"
         style="@style/ToolbarButton"
         android:layout_gravity="start|center_vertical"
         android:contentDescription="@string/close_tab" />
     <FrameLayout
         android:id="@+id/location_bar_frame_layout"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:layout_gravity="center_vertical" >
         <ImageButton
             android:id="@+id/security_button"
             style="@style/LocationBarButton"
             android:layout_width="@dimen/location_bar_icon_width"
             android:layout_height="match_parent"
             android:layout_gravity="center_vertical"
-            android:alpha="0"
             android:contentDescription="@string/accessibility_toolbar_btn_site_info"
             android:scaleType="center"
             android:visibility="gone" />
         <FrameLayout
             android:id="@+id/title_url_container"
             android:layout_width="match_parent"
             android:layout_height="wrap_content"
             android:layout_gravity="center_vertical"
             android:background="@null" >
             <TextView
@@ skipping 43 matching lines @@
         android:src="@drawable/btn_menu"
         android:contentDescription="@string/accessibility_toolbar_btn_menu"
         android:background="@null" />
     <org.chromium.chrome.browser.widget.ToolbarProgressBar
         android:id="@+id/progress"
         android:layout_width="match_parent"
         android:layout_height="2dp"
         chrome:progressBarColor="@color/progress_bar_foreground"
         chrome:backgroundColor="@color/progress_bar_background" />
 </org.chromium.chrome.browser.toolbar.CustomTabToolbar>