an easy example

1. open https://fonts.google.com/
2. set network throttle to Regular 2G under the network panel
3. reload page, all the responses are from memory cache or disk cache, yet the console is spammed with "Slow network is detected. Fallback font will be used while loading" messages

Able to reproduce the issue on the latest canary(60.0.3095.5) and the latest stable(58.0.3029.110) on Windows-10, Mac OS 10.12.4 and Linux Ubuntu 14.04.

Regressed in M-53.

Last good build: 53.0.2783.0
First bad build: 53.0.2784.0

Changelog:
==========
https://chromium.googlesource.com/chromium/src/+log/0f202ab267491fb469ffcb321560d9f0cfccf825..dbd9f219ef9b615d9e116964e46b1a390c9354a1

Suspecting: https://codereview.chromium.org/2087293003

dgozman@: Could you please take a look at this.

Thank you!

@toyoshim: could you please take a look?

could these messages be collapsed into a single expandable log entry?

Find the same messages in Chrome log file that the customer has provided.
Here is details about environment.
Chrome version: 62.0.3167.0 (64 bit)  Channel: canary
OS Version: Windows 10 version 1703
https://drive.google.com/open?id=0B01YYztUbOCua1RpVTFadTJJXzg

Currently we detect slow networks on loading the main resource or based on other network traffics until that time, and applies interventions against all font loadings.

So, this warning is intentional.

If the page author expects that the page will be visited by users who are on slow networks, the author needs to be careful about using WebFonts, e.g. loading it in a suitable timing not to interfere other first-paint-blocking resources, and setting CSS font-property correctly.

This is warnings for that.

but this is happening in a single page application, i.e. the page and the font has already been loaded

There is also a possibly related problem with Favicons
https://bugs.chromium.org/p/chromium/issues/detail?id=721635

One curious thing is the intervention is triggered even when the data is on memory cache. This is not by design.

Note, we are seeing similar behavior even when internet downloads speeds are 75Mb+/sec. That behavior also does not appear to be consistent with Comment #8 above.

Implementation details depend on platform, but we measure HTTP level round trip time to estimate network quality. So, even network is fast enough, if some responses take long time, Chrome mistakenly estimate that network is slow.

> zac.spitzer
I tried to reproduce this by visiting https://fonts.google.com over emulated slow network. But I just confirmed that only requests from disk caches show the log messages. Did you see the same log even for data from memory caches?

Also, now DevTools console has a feature to combine similar messages into one expandable packet. So I want to close this issue.

 Issue 765378  tracks the work for incorrect triggering of this feature on high speed connections. In some cases, the web servers may take too long to process network requests in which case Chrome may incorrectly compute the network quality as too slow.

Please track the  issue 765378  for triggered in fast networks issue.