RFR: 8277807: Increase default initial concurrent refinement threshold [v3]

[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 incrementally with one additional commit since the last revision:

  make magic value more prominent

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6549/files
  - new: https://git.openjdk.java.net/jdk/pull/6549/files/0adb6a5a..a3216eff

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6549&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6549&range=01-02

  Stats: 9 lines in 1 file changed: 4 ins; 3 del; 2 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