This patch simplifies argument validation in NsdManager public api and
regroup duplicated validation into common methods.
This makes stack traces more actionable as now specific errors will
cause the api to throw exception from specific methods, whereas before
IllegalArgumentException would be thrown from inside the same api method
for different reasons.
This patch also includes a couple of other small cleanups.
Test: $ runtest -x frameworks/base/tests/net/../NsdManagerTest.java
Bug: 37013369
(cherry picked from commit f2c64f8725)
Change-Id: Icf047532aa551fbe0a70721cfb95507eaa84d51e
38e4783a60