RFR(S): 8245011: Add JFR event for cold methods flushed

[Nils Eliasson]

Hi,

Please review this small patch that adds a JFR event for cold methods 
that are flushed and adds the total number of cold methods flushed to 
the sweeper statistics event.

Bug: https://bugs.openjdk.java.net/browse/JDK-8245011
Webrev: http://cr.openjdk.java.net/~neliasso/8245011/

Please review,

Nils Eliasson