8256072: Eliminate JVMTI tagmap rehashing

Reviewed-by: kbarrett, eosterlund

src/hotspot/share/oops/oop.cpp

@@ -99,10 +99,7 @@ void oopDesc::verify(oopDesc* oop_desc) {
 intptr_t oopDesc::slow_identity_hash() {
   // slow case; we have to acquire the micro lock in order to locate the header
   Thread* current = Thread::current();
-  ResetNoHandleMark rnm; // Might be called from LEAF/QUICK ENTRY
-  HandleMark hm(current);
-  Handle object(current, this);
-  return ObjectSynchronizer::identity_hash_value_for(object);
+  return ObjectSynchronizer::FastHashCode(current, this);
 }
 
 // used only for asserts and guarantees