[11u] RFR: 8237375: SimpleThresholdPolicy misses CounterDecay timestamp initialization

[Langer, Christoph]

Hi,

please help reviewing the backport of the following change to jdk11u:

Bug: https://bugs.openjdk.java.net/browse/JDK-8237375
Original change: https://hg.openjdk.java.net/jdk/jdk/rev/2a0e2304e68b
Webrev: http://cr.openjdk.java.net/~clanger/webrevs/8237375.11u/

Between 11 and head, src/hotspot/share/runtime/compilationPolicy.cpp was moved to src/hotspot/share/compiler/compilationPolicy.cpp. So, the backport goes to src/hotspot/share/runtime/compilationPolicy.cpp. The original change would furthermore not apply due to its predecessor "8235741: Inappropriate uses of os::javaTimeMillis()" which isn't backported. I had to do some context shifting and replace usage of method nanos_to_millis, since this was only introduced with 8235741.

Thanks
Christoph