Thanks for filing and working on the CL!

However, I'd like to understand whether we can use Network domain to actually receive the font resource for webfonts. WDYT?

Using the Network domain was my initial idea for how to implement this.
|Network.responseReceived| includes a |ResourceType| and |RequestId|.  One of the
|ResourceType|s is |Font|, and it looks like |RequestId| can be passed to
|Network.getResponseBody| to retrieve the response body, so that theoretically
connects the dots.

With using the Network domain however, the missing piece is how to connect this
back to all of the CSS styling information and metadata like resolved platform
font family, at the time the font is loaded.  The code change I have locally
extends my earlier CL in
https://chromium.googlesource.com/chromium/src/+/bf7bdf59830d9d9e48d73278457cc1e9173f702d%5E%21/#F14
to include the base64-encoded font.

I can post the CL shortly if you'd like to see what it looks like in practice.
I'm open to suggestions on other approaches.

Can we find a link from the SharedBuffer in which Blink holds the font blob to a RequestId - this way we could combine the Network Domain and the fonts event.

If that's impractical, how about a hash over the raw font data in the event? Then you could capture the ResourceType=Font matches and compare them by checksum to the one in the fontsUpdated event?

1. This approach will definitely introduce extra traffic, which I'd like to avoid. Most clients are not interested in the font data, but they will get huge payloads with it when enabling CSS domain. Network.getResponseBody is an explicit call, which mitigates this issue.

2. Can we match the request by url, to use Network.getResponseBody? I believe that blink will issue each FontFace.src just once, so there should be no confusion. Dominik should know better though.

3. We also have Page.getResourceContent method which can fetch the resource by url, so that you don't have to listen to all Network notifications to find the RequestId for the resource. Will that work for you?

Thanks for the suggestions.  I'm AFK next week, though will take a closer look
at these approaches when I am back.

I don't think anyone has enough cycles to do this, feel free to reopen once you have a patch!