Use DecorToolbar.getViewGroup() to get the view properly.

Bug: 15320825
Change-Id: Ib7e162c816fadf2b5c83af1326e7158f6bd69c8e
diff --git a/core/java/com/android/internal/app/WindowDecorActionBar.java b/core/java/com/android/internal/app/WindowDecorActionBar.java
index a0c75a6..5c7a4e6 100644
--- a/core/java/com/android/internal/app/WindowDecorActionBar.java
+++ b/core/java/com/android/internal/app/WindowDecorActionBar.java
@@ -342,7 +342,7 @@
     @Override
     public void setCustomView(int resId) {
         setCustomView(LayoutInflater.from(getThemedContext()).inflate(resId,
-                (ViewGroup) mDecorToolbar, false));
+                mDecorToolbar.getViewGroup(), false));
     }
 
     @Override