RFR: 8036699: Add trace event when a metaspace allocation fails

[Erik Helin]

Hi all,

this patch adds the new trace event vm/gc/metaspace/allocation_failure. 
The event will be sent when we get an allocation failure in metaspace. 
The event will contain the following information:
- classLoader - the class loader doing the allocation
- anonymousClassLoader - if the classLoader is anonymous
- nativeStackTrace - a VM stack trace (see more below)
- metadataType - the kind of metadata (class or non-class)
- metaspaceObjectType - the kind of metaspace object

The field nativeStackTrace will contain a string representation of the 
Threads C frames (up until the first Java frame). This is very useful 
for debugging metaspace allocation failures coming from VM internals 
such as the interpreter or GC code.

I would especially appreciate if someone could look over the code in 
metaspaceTracer.cpp performing the stack walking.

Webrev:
http://cr.openjdk.java.net/~ehelin/8036699/webrev.00/

Enhancement:
https://bugs.openjdk.java.net/browse/JDK-8036699

Testing:
- JFR JTREG tests
- JPRT
- Manual stress testing of the stack walking code by writing small test
   programs that causes metaspace allocation failures from both Java
   threads and non-Java threads.

Thanks,
Erik