JDK-8368159 added `JvmtiExport::has_frame_pops(JavaThread* thread)`
which calls `JvmtiExport::get_jvmti_thread_state();` which may safepoint.

Example stack trace:
```
V [libjvm.dylib+0x125f888] VMError::report(outputStream*, bool)+0x1b68 (javaThread.cpp:375)
V [libjvm.dylib+0x1263184] VMError::report_and_die(int, char const*, char const*, char*, Thread*, unsigned char*, void const*, void const*, char const*, int, unsigned long)+0x55c
V [libjvm.dylib+0x5de268] print_error_for_unit_test(char const*, char const*, char*)+0x0
V [libjvm.dylib+0x9427ec] JavaThread::check_for_valid_safepoint_state()+0x120
V [libjvm.dylib+0xe7e4e4] Mutex::lock(Thread*)+0x48
V [libjvm.dylib+0xbbb198] JvmtiThreadState::state_for(JavaThread*, Handle)+0x200
V [libjvm.dylib+0xc462ec] JvmtiEventControllerPrivate::thread_started(JavaThread*)+0x1a0
V [libjvm.dylib+0xc493a4] JvmtiExport::get_jvmti_thread_state(JavaThread*, bool)+0xc0
V [libjvm.dylib+0xc5078c] JvmtiExport::has_frame_pops(JavaThread*)+0x24
V [libjvm.dylib+0x59c398] freeze_epilog(JavaThread*, ContinuationWrapper&, freeze_result)+0xf8
V [libjvm.dylib+0x59b6e8] Config<(oop_kind)0, CardTableBarrierSet>::freeze(JavaThread*, long*)+0x6f4
V [libjvm.dylib+0x59a4d4] int freeze<Config<(oop_kind)0, CardTableBarrierSet>>(JavaThread*, long*)+0x108
```

I suggest we do double checked on `JvmtiExport::can_post_frame_pop()` and move the ContinuationWrapper::SafepointOp scope.