I removed the if check when making this code work with OOPIFs and earned the #1 renderer crash: https://bugs.chromium.org/p/chromium/issues/detail?id=803811

There was originally a DCHECK in the code: https://chromium.googlesource.com/chromium/src/+/1593920eed56dee727e7f78ae5d206052e4ad7e0/third_party/WebKit/Source/core/timing/PerformanceBase.cpp#362

but it seems we don't actually have test coverage of this case. I'm not very familiar with the resource timing code, but it does seem like we should try to get coverage of this if possible.