DO NOT MERGE AdapterView#isScrollableForAccessibility does not handle null adapter.

Cherry picking since branching caught us in the middle of review.

1. If an AdapterView has no adapter and the view tries to fire an
   accessibility event we get a null pointer exception.

bug:5439321

Change-Id: Ia3d7a5ad852ef42422d10d8a62c4d3af6792313b

Author: sganov

core/java/android/widget/AdapterView.java

@@ -928,9 +928,13 @@ public void onInitializeAccessibilityEvent(AccessibilityEvent event) {
     }
 
     private boolean isScrollableForAccessibility() {
-        final int itemCount = getAdapter().getCount();
-        return itemCount > 0
-            && (getFirstVisiblePosition() > 0 || getLastVisiblePosition() < itemCount - 1);
+        T adapter = getAdapter();
+        if (adapter != null) {
+            final int itemCount = adapter.getCount();
+            return itemCount > 0
+                && (getFirstVisiblePosition() > 0 || getLastVisiblePosition() < itemCount - 1);
+        }
+        return false;
     }
 
     @Override