Use floating labels for preference forms

chrome/android/java/res/layout/homepage_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. -->
 
 <ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:fillViewport="true"
     style="@style/PreferenceScreenLayout" >
 
     <LinearLayout
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:clickable="true"
         android:focusableInTouchMode="true"
         android:orientation="vertical"
-        android:paddingTop="6dp" >
+        android:paddingStart="@dimen/pref_homepage_layout_margin"
+        android:paddingEnd="@dimen/pref_homepage_layout_margin" >
 
         <LinearLayout
             android:layout_width="match_parent"
             android:layout_height="wrap_content"
-            android:layout_margin="6dp"
             android:orientation="horizontal" >
 
             <TextView
                 android:id="@+id/homepage_switch_label"
                 android:layout_width="0dp"
                 android:layout_weight="1"
                 android:layout_height="wrap_content"
                 android:singleLine="true"
                 android:textAppearance="@style/PreferenceTextAppearanceMedium" />
 
@@ skipping 22 matching lines @@
         <CheckBox
             android:id="@+id/default_checkbox"
             android:layout_width="match_parent"
             android:layout_height="wrap_content"
             android:layout_marginTop="6dp"
             android:layout_marginBottom="6dp"
             android:text="@string/homepage_default_title" />
     </LinearLayout>
 
 </ScrollView>