MDM Auto Fill Restriction

Implementation of MDM form auto fill restriction. When enforced,
the auto-fill menu item is greyed and unchecked, and if clicked,
results in the "Managed by your administrator" Toast message.

Disabling the restriction checks the menu item checkbox and ungreys
the menuitem, restoring full control of this feature to the user.

This patch also includes minor refactoring of DoNotTrackRestriction.

Change-Id: I2f36ea9263a70f0a9470900c3abc48d9376a4604
diff --git a/res/xml/general_preferences.xml b/res/xml/general_preferences.xml
index 7571a6a..75b4600 100644
--- a/res/xml/general_preferences.xml
+++ b/res/xml/general_preferences.xml
@@ -57,7 +57,7 @@
             android:summary="@string/pref_nightmode_enabled_summary"
             android:title="@string/pref_nightmode_enabled" />
 
-        <SwitchPreference
+        <com.android.browser.mdm.MdmCheckBoxPreference
             android:layout="@layout/swe_preference"
             android:key="autofill_enabled"
             android:title="@string/pref_autofill_enabled"