RFR: 8229517: Support for optional asynchronous/buffered logging [v2]

[Xin Liu]

> This patch provides a buffer to store asynchrounous messages and flush them to
> underlying files periodically.

Xin Liu has updated the pull request incrementally with two additional commits since the last revision:

 - 8229517: Support for optional asynchronous/buffered logging
   
   add a constraint for the option LogAsyncInterval.
 - 8229517: Support for optional asynchronous/buffered logging
   
   LogMessage supports async_mode.
   remove the option AsyncLogging
   renanme  the option GCLogBufferSize to AsyncLogBufferSize
   move drop_log() to LogAsyncFlusher.

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/3135/files
  - new: https://git.openjdk.java.net/jdk/pull/3135/files/28718943..bcefbecb

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3135&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3135&range=00-01

  Stats: 120 lines in 8 files changed: 84 ins; 11 del; 25 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3135.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3135/head:pull/3135

PR: https://git.openjdk.java.net/jdk/pull/3135