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