[Payments] Animates EditorView in and out

chrome/android/java/res/layout/payment_request_editor.xml

 <?xml version="1.0" encoding="utf-8"?>
 <!-- Copyright 2016 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. -->
 
 <!-- PaymentRequestUI editor dialog. -->
 <RelativeLayout
     xmlns:android="http://schemas.android.com/apk/res/android"
-    xmlns:chrome="http://schemas.android.com/apk/res-auto" >
+    xmlns:chrome="http://schemas.android.com/apk/res-auto"
+    android:background="@android:color/white" >
 
     <!-- Toolbar -->
     <org.chromium.chrome.browser.payments.ui.EditorDialogToolbar
         android:id="@+id/action_bar"
         android:layout_width="match_parent"
         android:layout_height="?attr/actionBarSize"
         android:layout_alignParentTop="true"
         android:layout_alignParentStart="true"
         android:layout_alignParentEnd="true"
         android:background="@color/dark_action_bar_color" />
@@ skipping 21 matching lines @@
     <!-- Shadow overlaps the FadingEdgeScrollView. -->
     <org.chromium.chrome.browser.widget.FadingShadowView
         android:id="@+id/shadow"
         android:layout_width="match_parent"
         android:layout_height="@dimen/action_bar_shadow_height"
         android:layout_below="@id/action_bar"
         android:layout_alignParentStart="true"
         android:layout_alignParentEnd="true" />
 
 </RelativeLayout>