RFR: 8183545: Event tracing, transition hooks

[Robbin Ehn]

Hi all,

Please review.

This patch adds a new bit in suspend flag for the tracing backend.
Thus tracing backend can suspend threads on certain transitions.

(David H and Dan D have looked at this, that's why they are on CC)

I have also put in a oneliner in:
src/share/vm/classfile/javaClasses.cpp

Which adds Threads_lock->owned_by_self() to the assert.
Threads_lock->owned_by_self() give the same guarantees as is_Watcher_thread(), e.g. there is no safepoint.

If you really insist I can put the oneliner in a separate issue, but the tracing backend changes depends on both.

Issue: https://bugs.openjdk.java.net/browse/JDK-8183545
Webrev: http://cr.openjdk.java.net/~rehn/8183545/webrev/index.html

Test: openjdk build on Linux x64

Thanks!

/Robbin