[Payments] Update billing address dropdown style to match the design

chrome/android/java/res/layout/payment_request_editor_dropdown.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. -->
 
 <LinearLayout
         xmlns:android="http://schemas.android.com/apk/res/android"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:layout_marginTop="@dimen/payments_section_large_spacing"
         android:layout_marginBottom="@dimen/payments_section_large_spacing"
         android:layout_marginStart="@dimen/pref_autofill_field_horizontal_padding"
         android:layout_marginEnd="@dimen/pref_autofill_field_horizontal_padding"
         android:orientation="vertical">
 
     <TextView
             android:id="@+id/spinner_label"
             android:layout_width="match_parent"
             android:layout_height="wrap_content"
             android:textAppearance="@style/PreferenceFloatLabelTextAppearance" />
 
     <android.support.v7.widget.AppCompatSpinner
             android:id="@+id/spinner"
-            android:layout_width="fill_parent"
+            android:layout_width="match_parent"
             android:layout_height="wrap_content"
-            android:layout_marginTop="@dimen/pref_autofill_field_top_margin" />
+            android:layout_marginTop="@dimen/pref_autofill_field_top_margin"
+            android:dropDownWidth="match_parent" />

[Ian Wen, 2016/12/20 21:52:23]

Q: how does this look on tablets? On Nexus 10 will be tiny texts with huge blank
space?

[gogerald1, 2016/12/21 00:36:34]

I think it's fine since the spinner width is large as well. Attached two
screenshots from Nexus 7 on the bug.

 
     <View style="@style/PreferenceSpinnerUnderlineView" />
 
 </LinearLayout>