hg: jdk/jdk12: 8215451: JNI IsSameObject should not keep objects alive

[per.liden at oracle.com]

Changeset: 7aa1a37b04a2
Author:    pliden
Date:      2018-12-17 16:55 +0100
URL:       http://hg.openjdk.java.net/jdk/jdk12/rev/7aa1a37b04a2

8215451: JNI IsSameObject should not keep objects alive
Reviewed-by: eosterlund, kbarrett

! src/hotspot/share/prims/jni.cpp
! src/hotspot/share/runtime/jniHandles.cpp
! src/hotspot/share/runtime/jniHandles.hpp
! src/hotspot/share/runtime/jniHandles.inline.hpp
! test/hotspot/jtreg/serviceability/jvmti/HeapMonitor/MyPackage/HeapMonitorThreadTest.java