Worth noting that this is potentially a pretty big undertaking - it would have to be plumbed through all ResourceHAndlers, ResourceThrottles, extensions, etc, some of which probably don't currently expect multiple sets of headers.

Also, one weirdness here is that if the response is cached, then we lose all 103 hints (Weird!)

Do servers currently support early hints? I've surfed the net a bit and neither google.com nor gmail.com send the header 103. I've added log right here - https://cs.chromium.org/chromium/src/net/spdy/spdy_stream.cc?l=438 

Does any body know a good set up in order to test early hints? AFAIK, npm supports that, but I need to add https there in order to establish http/2

There's a test endpoint up at https://nghttp2.org/?103-eh

FYI, this is likely to be an RFC soon.

WRT the concern that the cached response loses the hints -- the spec is worded to indicate that they're hints of headers that will appear in the final response, so when that's the case, they will be cached.

For reference, this has indeed been published as RFC8297: https://tools.ietf.org/html/rfc8297.

Firefox implementing: https://bugzilla.mozilla.org/show_bug.cgi?id=1407355

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d611ebfba50d215d4257ee89b4ef890a016d31b2

commit d611ebfba50d215d4257ee89b4ef890a016d31b2
Author: Bence Béky <bnc@chromium.org>
Date: Thu Jun 07 04:34:34 2018

Add Net.SpdyResponseCode histogram to track HTTP/2 response codes.

This would be useful to see how often servers send a 103 Early Hints
response (to be able to better prioritize implementing support), and to
see how often servers send a 101 Switching Protocols response (which
means their WebSocket over HTTP/2 implementation is broken), and a whole
bunch of other things.

Bug: 671310, 801564
Change-Id: I9e66acb6405793c4b3c12cf9d5b32edb2262c70b
Reviewed-on: https://chromium-review.googlesource.com/1087583
Reviewed-by: Zhongyi Shi <zhongyi@chromium.org>
Reviewed-by: Gayane Petrosyan <gayane@chromium.org>
Commit-Queue: Bence Béky <bnc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#565179}
[modify] https://crrev.com/d611ebfba50d215d4257ee89b4ef890a016d31b2/net/spdy/spdy_stream.cc
[modify] https://crrev.com/d611ebfba50d215d4257ee89b4ef890a016d31b2/tools/metrics/histograms/enums.xml
[modify] https://crrev.com/d611ebfba50d215d4257ee89b4ef890a016d31b2/tools/metrics/histograms/histograms.xml

I'm not sure how much useful data this is going to give you, considering that sites won't start emitting 103 until browsers do something useful with it. (insert comment about chickens and eggs).

I need fast Internet. Faster response. More speed. I am not satisfied with how browsers are slow nowadays. Make the response time faster and you will revoltionize the Internet.