[SuwLib] Fix TintedDrawable

Mark the drawable as isStateful, so that state updates will be
propagated from TextView to the drawable.

Bug: 26904125
Change-Id: Ieffb49242f802753e64ba4ef997da48ba34ba05b

library/eclair-mr1/src/com/android/setupwizardlib/view/NavigationBarButton.java

@@ -123,6 +123,11 @@ public class NavigationBarButton extends Button {
             super(new Drawable[] { wrapped });
         }
 
+        @Override
+        public boolean isStateful() {
+            return true;
+        }
+
         @Override
         public boolean setState(int[] stateSet) {
             boolean needsInvalidate = super.setState(stateSet);