[SetupWizardLib] Post checkScroll in BottomScrollView

In BottomScrollView, post the checkScroll instead of running it
immediately from onLayout, so that views that change within the
callbacks will be re-laid-out.

Bug: 19635676
Change-Id: I0c8b47abd8c40c0c44da8498e1397b1940cce0b3

library/src/com/android/setupwizardlib/view/BottomScrollView.java

@@ -37,6 +37,13 @@ public class BottomScrollView extends ScrollView {
     private int mScrollThreshold;
     private boolean mRequiringScroll = false;
 
+    private final Runnable mCheckScrollRunnable = new Runnable() {
+        @Override
+        public void run() {
+            checkScroll();
+        }
+    };
+
     public BottomScrollView(Context context) {
         super(context);
     }
@@ -62,7 +69,10 @@ public class BottomScrollView extends ScrollView {
                     - getPaddingBottom());
         }
         if (b - t > 0) {
-            checkScroll();
+            // Post check scroll in the next run loop, so that the callback methods will be invoked
+            // after the layout pass. This way a new layout pass will be scheduled if view
+            // properties are changed in the callbacks.
+            post(mCheckScrollRunnable);
         }
     }