RFR: 8182284: G1Analytics uses uninitialized fields

[Erik Helin]

Hi all,

this small patch just initializes two uninitialized fields in 
G1Analytics. 0.0 is a good enough as starting value, the fields are not 
meant to be read before a GC has been run (but if this would happen, 
observing 0.0 fits together with the calculations that the values 
represents).

Bug:
https://bugs.openjdk.java.net/browse/JDK-8182284

Webrev:
http://cr.openjdk.java.net/~ehelin/8182284/00/

Testing:
- Mach5 hs-tier1,hs-tier2
- Newly added unit test

Thanks,
Erik