Use explicit dividers between preferences in AccountManagementFragment

chrome/android/java/res/xml/account_management_preferences.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. -->
 
 <PreferenceScreen
     xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:app="http://schemas.android.com/apk/res-auto"
     android:orderingFromXml="false">
 
     <PreferenceCategory
         android:title="@string/account_management_title"
         android:order="0" />
 
     <!-- Google accounts will be inserted here, using order values starting at 100 -->
 
     <org.chromium.chrome.browser.preferences.ChromeBasePreference
         android:key="add_account"
         android:icon="@drawable/add_circle_blue"
         android:order="1000" />
 
+    <Preference
+        android:layout="@layout/divider_preference"
+        android:order="1001" />
+
     <PreferenceCategory
         android:key="parental_settings"
         android:title="@string/account_management_parental_settings"
-        android:order="1001" />
+        android:order="1002" />
 
     <org.chromium.chrome.browser.preferences.ChromeBasePreference
         android:key="parent_accounts"
-        android:order="1002" />
+        android:order="1003" />
 
     <Preference
         android:key="child_content"
         android:title="@string/account_management_child_content_title"
-        android:order="1003" />
+        android:order="1004" />
+
+    <Preference
+        android:key="child_content_divider"
+        android:layout="@layout/divider_preference"
+        android:order="1005" />
 
     <org.chromium.chrome.browser.preferences.SyncPreference
         android:key="sync_settings"
         android:title="@string/sign_in_sync"
-        android:order="1005"/>
+        android:order="1006" />
+
+    <Preference
+        android:layout="@layout/divider_preference"
+        android:order="1007" />
 
     <Preference
         android:key="google_activity_controls"
         android:icon="@drawable/googleg"
         android:title="@string/sign_in_google_activity_controls"
         android:summary="@string/sign_in_google_activity_controls_message"
-        android:order="1006" />
+        android:order="1008" />
+
+    <Preference
+        android:layout="@layout/divider_preference"
+        android:order="1009" />
 
     <Preference
         android:key="sign_out"
         android:title="@string/account_management_sign_out"
-        android:order="1007"/>
+        android:order="1010" />
+
+    <Preference
+        android:key="sign_out_divider"
+        android:layout="@layout/divider_preference"
+        android:order="1011" />
 
 </PreferenceScreen>