RFR (S): 8239593: Bogus warning "Re-registering of platform native method" for a JVMTI agent

[David Holmes]

Bug: https://bugs.openjdk.java.net/browse/JDK-8239593
webrev: http://cr.openjdk.java.net/~dholmes/8239593/webrev/

The original intent was to warn if changes were being made to platform 
classes by non-platform classes. That was weakened slightly to warn if 
classes loaded by the boot/platform loaders were modified by a class not 
loaded by the boot/platform loader. But that formulation also catches 
non-platform classes that have been added to the bootclasspath. So we 
augment the check to also check that the target class is in a named 
module** (loaded by the boot/platform loader) - this ensures we catch 
changes to platform files whilst excluding classes incidentally on the 
bootclasspath.

** Note that you cannot add a named module to the boot/platform loaders 
at runtime - they are defined at build time.

Tested against Yourkit reproducer in the bug report, and with existing 
registerNatives test.

Test builds on tier1 platforms.

Thanks,
David