Make View#setBackgroundDrawable a no-op if setting the same background.

Change-Id: Idd3e0ae80609557d82a5564daa1cfb0abca42ded
diff --git a/core/java/android/view/View.java b/core/java/android/view/View.java
index 2a65f0c..41b9e2d 100644
--- a/core/java/android/view/View.java
+++ b/core/java/android/view/View.java
@@ -11122,6 +11122,10 @@
      *        background
      */
     public void setBackgroundDrawable(Drawable d) {
+        if (d == mBGDrawable) {
+            return;
+        }
+
         boolean requestLayout = false;
 
         mBackgroundResource = 0;