RFR(X): 8195818: JFR.start should increase autogenerated name by one

[Erik Gahlin]

Hi,

Could I please have a review of this fix.

Problem is that the recording id is increased by one, if a user makes a 
dump. It should only increase if you start a new recording.

This happens because internally a clone is created to mimic what would 
happen if a users stopped the recording with a filename. This is an 
implementation detail that leaks out.

Fix is to use PlatformRecording class, which is the internal 
implementation, instead the Recording class which is the public API. 
Since this happens when the recorder lock is held, a user will never be 
able to see this short temporary recording, so it is safe to reuse the 
id (0) for all such recordings. The initial id 1.

Bug:
https://bugs.openjdk.java.net/browse/JDK-8195818

Webrev:
http://cr.openjdk.java.net/~egahlin/8195818.1/

Testing:
Tests in test/jdk/jdk/jfr

Thanks
Erik