Bug 1201206 - Correct menu button background on 2.3. r=mhaigh

One fear is that different devices set different menu colors and text colors.
Since we're using the default text color and set an explicit menu color, the
text color may not look good on these devices. I was unable to find a way to
override the menu text color.

It seems the best way to find out if this is a problem is to land
it and test though!

--HG--
extra : commitid : ylxnVEA269
extra : source : c01f712e3d98c74a03f1dcf9c5133c0c8982d32d

mobile/android/base/resources/values/colors.xml

@@ -154,4 +154,7 @@
 
   <color name="private_active_text">#FFFFFF</color>
 
+  <!-- This color is from a 2.3 Samsung device. -->
+  <color name="gingerbread_menu_background_color">#1b1b1b</color>
+
 </resources>

mobile/android/base/resources/values/themes.xml

@@ -12,6 +12,10 @@
     <style name="GeckoBase" parent="Theme.AppCompat.Light.DarkActionBar">
         <item name="android:windowNoTitle">true</item>
         <item name="android:windowContentOverlay">@null</item>
+
+        <!-- AppCompat sets this to transparent by default:
+             http://stackoverflow.com/a/31777488 -->
+        <item name="android:panelBackground">@color/gingerbread_menu_background_color</item>
     </style>
 
     <style name="GeckoDialogBase" parent="@android:style/Theme.Dialog">