Use floating labels for preference forms

chrome/android/java/res/values/dimens.xml

Index: chrome/android/java/res/values/dimens.xml
diff --git a/chrome/android/java/res/values/dimens.xml b/chrome/android/java/res/values/dimens.xml
index d7d0e6a6b5fea1b1bd98543b83129af535170444..ee7a18a60d9262ff391c9b35b26203f8c24a19dd 100644
--- a/chrome/android/java/res/values/dimens.xml
+++ b/chrome/android/java/res/values/dimens.xml
@@ -90,14 +90,15 @@
     <dimen name="password_generation_horizontal_margin">10dp</dimen>
     <dimen name="password_generation_text_vertical_margin">12dp</dimen>
 
-    <!--  Preferences button dimensions -->
-    <!-- TODO(twellington): Remove/update the following dimens after we switch the PreferencesTheme
-                                parent to AppCompat. -->
+    <!--  Preferences dimensions -->
+    <!-- TODO(twellington): Remove/update the button dimens after AppCompat adds button support. -->
     <dimen name="pref_button_margin_start">0dp</dimen>
     <dimen name="pref_button_corner_radius">2dp</dimen>
     <dimen name="pref_button_horizontal_padding">16dp</dimen>
     <dimen name="pref_button_vertical_padding">10dp</dimen>
 
+    <dimen name="pref_homepage_layout_margin">10dp</dimen>
+
     <!-- Minimum height/width for a touchable item -->
     <dimen name="min_touch_target_size">48dp</dimen>