Add a method to get the visiblity of BottomActionBar

Test: Manually
Bug: 151287328
Change-Id: I8459793f1ec506d4abf329377e774ed847989580
diff --git a/src/com/android/wallpaper/widget/BottomActionBar.java b/src/com/android/wallpaper/widget/BottomActionBar.java
index ee68b81..77b1bba 100644
--- a/src/com/android/wallpaper/widget/BottomActionBar.java
+++ b/src/com/android/wallpaper/widget/BottomActionBar.java
@@ -159,6 +159,10 @@
         }
     }
 
+    /** Returns {@code true} if visible. */
+    public boolean isVisible() {
+        return getVisibility() == VISIBLE;
+    }
 
     /** Shows {@link BottomActionBar}. */
     public void show() {