RFR: 8202711: Merge tiered compilation policies

[Claes Redestad]

Hi,

the simple and advanced threshold policy for tiered compilation should 
be merged into a single policy.

I suggest merging all redefined code in AdvancedThresholdPolicy into 
SimpleThresholdPolicy:

Bug: https://bugs.openjdk.java.net/browse/JDK-8202711
Webrev: http://cr.openjdk.java.net/~redestad/8202711/open.00/

As a follow-up we should consider renaming this to TieredCompPolicy (to 
be consistent with NonTieredCompPolicy) or TieredCompilationPolicy.

Thanks!

/Claes