Bug 771159 - Properly set toolbar's background size to handle different densities (r=mfinkle)

mobile/android/themes/core/aboutReader.css

@@ -335,6 +335,7 @@ body {
   }
 
   .toolbar {
+    background-size: 48px;
     background-image: url('chrome://browser/skin/images/reader-toolbar-bg-port-mdpi.png');
   }
 
@@ -355,6 +356,7 @@ body {
   }
 
   .toolbar {
+    background-size: 40px;
     background-image: url('chrome://browser/skin/images/reader-toolbar-bg-land-mdpi.png');
   }
 
@@ -375,6 +377,7 @@ body {
   }
 
   .toolbar {
+    background-size: 56px;
     background-image: url('chrome://browser/skin/images/reader-toolbar-bg-xlarge-mdpi.png');
   }