I've done tests with straight calls to getaddrinfo and I do see some of them taking over 400ms on the same device as was used for Cronet tests. 
It is fairly sporadic though, with most taking under 100ms.

In the logs Andrei gathered, it was very consistent, but possibly it depends upon whether it's in the device's cache?  I'm fairly sure these domain names would not have been in the OS cache.

One option which may improve performance is to try dns_sd.h instead of getaddrinfo.

https://opensource.apple.com/source/mDNSResponder/mDNSResponder-541/mDNSShared/dns_sd.h

Looking at dns_sd.h the DNSServiceGetAddrInfo is an interesting function, especially considering that it should provide more details, including ttl, but I could not get it to return anything meaningful neither on the physical device, nor on simulator. :(

I've added (https://chromium-review.googlesource.com/580398) tests that use NSURLSession with Cronet and platform stack to connect to <random>.googlevideo.com hosts (to avoid cached responses) and results are very comparable.

First run:

Cronet:

[0720/162000.040483:INFO:cronet_http_test.mm(162)] Elapsed Average:54.472ms Max:1067.58ms
[       OK ] HttpTest.NSURLSessionGoogleVideo (13770 ms)

Platform:

[0720/162013.454000:INFO:cronet_http_test.mm(191)] Elapsed Average:52.8421ms Max:1054.17ms
[       OK ] HttpTest.NSURLSessionGoogleVideoPlatform (13405 ms)

Second run:

Cronet:

[0720/162510.340800:INFO:cronet_http_test.mm(160)] Elapsed Average:50.3569ms Max:1053.46ms
[       OK ] HttpTest.NSURLSessionGoogleVideo (12736 ms)

Platform:

[0720/162531.391129:INFO:cronet_http_test.mm(189)] Elapsed Average:83.4414ms Max:4078.59ms
[       OK ] HttpTest.NSURLSessionGoogleVideoPlatform (21045 ms)

DNS response usually takes about 50ms, but sometimes slows all the way down to 1-4 seconds.
There is no significant difference between cronet and platform dns resolution performance.

Thanks for trying this out Misha.  I followed up with the people who suggested it to see if they have any other ideas.

Closing for now. We can reopen it when we have new information.