RFR: 8277807: Increase default initial concurrent refinement threshold [v4]

[Kim Barrett]

> Please review this change to the default initial concurrent refinement
> threshold.  The new value takes into account options that should provide a
> starting point that is closer to the long-term range.
> 
> Testing:
> mach5 tier1
> manually verified logged initial value matched expectations.

Kim Barrett has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:

 - Merge branch 'master' into init_green
 - make magic value more prominent
 - update copyright
 - increase default initial green zone value

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6549/files
  - new: https://git.openjdk.java.net/jdk/pull/6549/files/a3216eff..e9595bea

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6549&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6549&range=02-03

  Stats: 43897 lines in 1204 files changed: 26936 ins; 9502 del; 7459 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6549.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6549/head:pull/6549

PR: https://git.openjdk.java.net/jdk/pull/6549