6976636: JVM/TI test ex03t001 fails assertion

Reviewed-by: dcubed, dsamersoff

src/share/vm/prims/jvmtiExport.cpp

@@ -995,7 +995,9 @@ void JvmtiExport::post_class_unload(Klass* klass) {
         // Before we call the JVMTI agent, we have to set the state in the
         // thread for which we are proxying.
         JavaThreadState prev_state = real_thread->thread_state();
-        assert(prev_state == _thread_blocked, "JavaThread should be at safepoint");
+        assert(((Thread *)real_thread)->is_ConcurrentGC_thread() ||
+               (real_thread->is_Java_thread() && prev_state == _thread_blocked),
+               "should be ConcurrentGCThread or JavaThread at safepoint");
         real_thread->set_thread_state(_thread_in_native);
 
         jvmtiExtensionEvent callback = env->ext_callbacks()->ClassUnload;