Set the window backgrond and remove it in onCreate().

To have better transistion when launching the app.

bug: 6494653
Change-Id: I0f28796d599931c676c99e8f19a9f34e05018570
diff --git a/res/values/styles.xml b/res/values/styles.xml
index d619938..3c32cef 100644
--- a/res/values/styles.xml
+++ b/res/values/styles.xml
@@ -19,7 +19,7 @@
         <item name="android:displayOptions"></item>
         <item name="android:windowContentOverlay">@null</item>
         <item name="android:actionBarStyle">@style/Holo.ActionBar</item>
-        <item name="android:windowBackground">@null</item>
+        <item name="android:windowBackground">@android:color/black</item>
         <item name="android:colorBackground">@null</item>
         <item name="android:colorBackgroundCacheHint">@null</item>
     </style>