Add YUV element convenience function.

Change-Id: Ie67dfba6a4c4f1913875ad9817c53e45d56809ae
diff --git a/graphics/java/android/renderscript/Element.java b/graphics/java/android/renderscript/Element.java
index 3838c61..68badfa 100644
--- a/graphics/java/android/renderscript/Element.java
+++ b/graphics/java/android/renderscript/Element.java
@@ -725,6 +725,13 @@
         return rs.mElement_LONG_4;
     }
 
+    public static Element YUV(RenderScript rs) {
+        if (rs.mElement_YUV == null) {
+            rs.mElement_YUV = createPixel(rs, DataType.UNSIGNED_8, DataKind.PIXEL_YUV);
+        }
+        return rs.mElement_YUV;
+    }
+
     public static Element MATRIX_4X4(RenderScript rs) {
         if(rs.mElement_MATRIX_4X4 == null) {
             rs.mElement_MATRIX_4X4 = createUser(rs, DataType.MATRIX_4X4);