Show wallpaper as background for WifiSetupActivity

b/62571086

Before this change, WifiSetupActivity's UI was overlaying atop whichever
Activity was below it in the task, so the user saw two Activities at the
same time. With this change, the Activity is now properly backed by the
wallpaper, and can now safely be shown atop other Activities.

test: manual
Change-Id: If166db5f8f8f3423aad6fc9f8d385937033b9f5d
(cherry picked from commit 1d5ca9c532aa1305d5e4a42a929d34b2b433bb7f)
diff --git a/Settings/res/values/styles.xml b/Settings/res/values/styles.xml
index 108d92e..2a71329 100644
--- a/Settings/res/values/styles.xml
+++ b/Settings/res/values/styles.xml
@@ -55,8 +55,8 @@
         <item name="wifi_signal_color">@color/setup_list_item</item>
         <item name="wps_color">@color/setup_list_item</item>
         <item name="android:windowBackground">@android:color/transparent</item>
-        <item name="android:windowIsTranslucent">true</item>
         <item name="android:windowAnimationStyle">@style/SetupWindowAnimationStyle</item>
+        <item name="android:windowShowWallpaper">true</item>
     </style>
 
     <style name="Theme.Settings.Transparent">