Fix JDWP race at runtime shutdown

When the runtime shuts down, it closes the JDWP connection with the
debugger. However, if a JDWP command is still being processed by the
JDWP handler thread when we close the connection, we won't be able to
send its reply.

Bug: 19628620
Change-Id: I20301325a347d66f3b9ef95ebe8f156abafb1f76
6 files changed