RFR (XS) 8210347 : Combine subsequent calls to Set.contains() and Set.add()

[Ivan Gerasimov]

Hello!

It's a pico-optimization.
In a few places a call to Set.contains() can be merged with the 
following Set.add().

BUGURL: https://bugs.openjdk.java.net/browse/JDK-8210347

WEBREV: http://cr.openjdk.java.net/~igerasim/8210347/00/webrev/

Would you please help review the trivial fix?

--
With kind regards,
Ivan Gerasimov