Use framework support to reserve icon space

Framework now has iconSpaceReserved attr to support reserving icon
space. We no longer need to use a custom layout for each preference.

What's removed:
- custom style for normal preference
- custom layout/style for dropdown preference
- custom style for EditTextPreference

Fix: 37572422
Test: visual
Change-Id: I48d2997e6269143f58c2edd2d9902cdc0519ed04

res/layout/preference_dropdown_material_settings.xml

@@ -1,35 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<!--
-  Copyright (C) 2016 The Android Open Source Project
-
-  Licensed under the Apache License, Version 2.0 (the "License");
-  you may not use this file except in compliance with the License.
-  You may obtain a copy of the License at
-
-       http://www.apache.org/licenses/LICENSE-2.0
-
-  Unless required by applicable law or agreed to in writing, software
-  distributed under the License is distributed on an "AS IS" BASIS,
-  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-  See the License for the specific language governing permissions and
-  limitations under the License.
-  -->
-
-
-<!-- Based off frameworks/base/core/res/res/layout/preference_dropdown_material.xml
-     except that icon space in this layout is always reserved -->
-<FrameLayout
-    xmlns:android="http://schemas.android.com/apk/res/android"
-    android:layout_width="match_parent"
-    android:layout_height="wrap_content">
-
-    <Spinner
-        android:id="@+id/spinner"
-        android:layout_width="0dp"
-        android:layout_height="wrap_content"
-        android:layout_marginStart="@dimen/preference_no_icon_padding_start"
-        android:visibility="invisible" />
-
-    <include layout="@layout/preference_material_settings"/>
-
-</FrameLayout>

res/values/styles_preference.xml

@@ -28,11 +28,11 @@
     </style>
 
     <!-- Preferences -->
-    <style name="SettingsPreference">
+    <style name="SettingsPreference" parent="@style/Preference.Material">
         <item name="allowDividerAbove">false</item>
         <item name="allowDividerBelow">true</item>
         <item name="singleLineTitle">false</item>
-        <item name="android:layout">@layout/preference_material_settings</item>
+        <item name="iconSpaceReserved">true</item>
     </style>
 
     <style name="ApnPreference" parent="SettingsPreference">
@@ -48,13 +48,11 @@
            parent="@style/Preference.DialogPreference.EditTextPreference.Material">
         <item name="allowDividerAbove">false</item>
         <item name="allowDividerBelow">true</item>
-        <item name="android:layout">@layout/preference_material_settings</item>
+        <item name="iconSpaceReserved">true</item>
         <item name="android:dialogLayout">@layout/preference_dialog_edittext</item>
     </style>
 
-    <style name="SettingsDropdownPreference" parent="SettingsPreference">
+    <style name="SettingsDropdownPreference" parent="SettingsPreference" />
-        <item name="android:layout">@layout/preference_dropdown_material_settings</item>
-    </style>
 
     <style name="SettingsDialogPreference" parent="SettingsPreference" />