RFR(S): 8227225: ParallelGC: add subspace transitions for young gen for gc+heap=info log lines

[Kim Barrett]

> On Jul 29, 2019, at 10:41 AM, Tony Printezis <tprintezis at twitter.com> wrote:
> 
> Hi Thomas,
> 
> Latest webrev here:
> 
> http://cr.openjdk.java.net/~tonyp/8227225/webrev.1/
> 
> Main change: I renamed the PreGCValues class to PreGenGCValues so that it’s
> clear it’s mainly for generational GCs.

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src/hotspot/share/gc/shared/preGCValues.hpp 
  63   const size_t _young_gen_used;
  64   const size_t _young_gen_capacity;
  65   const size_t _eden_used;
  66   const size_t _eden_capacity;
  67   const size_t _from_used;
  68   const size_t _from_capacity;
  69   const size_t _old_gen_used;
  70   const size_t _old_gen_capacity;
  71   const metaspace::MetaspaceSizesSnapshot _meta_sizes;

Making these members const prevents assignment by the default
assignment operator.  I don't know if that's intentional, but it seems
unnecessary.

The _meta_sizes const qualifier is pre-existing.

------------------------------------------------------------------------------

Other than that, looks good.  I don't need a new webrev if you decide
to remove those const qualifiers.