RFR (S) 8250589: Move Universe::_reference_pending_list into OopHandle

[Kim Barrett]

> On Jul 27, 2020, at 10:10 AM, coleen.phillimore at oracle.com wrote:
> On 7/27/20 9:21 AM, Aleksey Shipilev wrote:
>> On 7/27/20 3:05 PM, coleen.phillimore at oracle.com wrote:
>> *) The change below implicitly tests for NULL now? Seems like _reference_pending_list.peek() would
>> be more efficient here, as it would not ask GC to keep the oop alive (especially when it is
>> guaranteed to be already alive, right?).
>> 
>>  bool Universe::has_reference_pending_list() {
>>    assert_pll_ownership();
>> -  return _reference_pending_list != NULL;
>> +  return _reference_pending_list.resolve();
>>  }
>> 
> This can be peek().  I'll change it.

HotSpot Style Guide says not to use implicit conversions to bool.
The “!= NULL” was intentional and should be retained.