Get failing WordIterator unit tests to pass again

WordIterator is now following the pattern in java.text.BreakIterator,
throwing an IllegalArgumentException when receiving an invalid argument.
Previously, it failed inconsistently.

Also add @SmallTest annotations to the WordIterator tests.

Bug: 29868991
Change-Id: I8158f2f419c8c4467205031655c0e62cc9ef5c1c
2 files changed