RFR: 8268852: AsyncLogWriter should not overide is_Named_thread()

[Xin Liu]

AsyncLogWriter is a subclass of NonJavaThread but not NamedThread. Therefore, 
is_Named_thread() must not return true.

Testing: 

1. hardcrash scenario:
...
Other Threads:
  0x00007f2870391f70 VMThread "VM Thread" [stack: 0x00007f2809d7d000,0x00007f2809e7d000] [id=76015]
  0x00007f28706a1d70 WatcherThread [stack: 0x00007f28082f0000,0x00007f28083f0000] [id=76033]
  0x00007f28702499b0 AsyncLog Thread [stack: 0x00007f2809e7f000,0x00007f2809f7f000] [id=76014]
...

2. jcmd $pid Thread.print
...
"AsyncLog Thread" os_prio=0 cpu=1015.24ms elapsed=181.04s tid=0x00007f7b14c57fb0 nid=0x12ed8 runnable
...

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

Commit messages:
 - 8268852: AsyncLogWriter should not overide is_Named_thread()

Changes: https://git.openjdk.java.net/jdk/pull/4503/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4503&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8268852
  Stats: 4 lines in 2 files changed: 2 ins; 1 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4503.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4503/head:pull/4503

PR: https://git.openjdk.java.net/jdk/pull/4503