Make isAssignableFrom not cast iftable entries to class.

The cast is unnecessary, and this change speeds up isAssignableFrom by
about 5%.

Bug: 22409569

(cherry-picked from commit 86ea497b965fe86d084e109e6d2d1ff560e8f4bf)

Change-Id: Ie5b7ebf4da6f75997bd80a8e19063ae2f84c7fef
1 file changed