My analysis so far:
For cross-origin sync XHR (at least), redirections happen in ThreadableLoader, which overrides the original ResourceRequest when it calls[1] LoadRequest. I couldn't find a way to get a hold of the original ResourceRequest at GenerateResourceTiming [2].

yhirano@ - Is ThreadableLoader doing that for other types of XHR/Fetch as well? (just to understand how common we should expect the problem to be)
Is there an easy way to avoid doing those redirections in a way that overrides the origin ResourceRequest?

One way I can think of to solve this is to keep a copy of the old ResourceRequest (or at least its URL) and consult that for the name property. Does that make sense?

[1] https://cs.chromium.org/chromium/src/third_party/blink/renderer/core/loader/threadable_loader.cc?type=cs&g=0&l=463
[2] https://cs.chromium.org/chromium/src/third_party/blink/renderer/core/timing/performance.cc?q=GenerateResourceTiming&sq=package:chromium&g=0&l=487

I think so.

If this issue is not urgent, out-of-blink CORS will fix it.

When is that supposed to land?

We're running finch on Canary. See issue 736308.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5ba90c2f9ee6e23c0ff0b22bc4ef0ae9477c57ad

commit 5ba90c2f9ee6e23c0ff0b22bc4ef0ae9477c57ad
Author: Yoav Weiss <yoavweiss@chromium.org>
Date: Wed Jan 16 18:06:39 2019

[Resource-Timing] `name` is wrong for http to https redirection

According to the spec, the `name` attribute MUST provide the
pre-redirection URL. In the case of http=>https redirections,
that's not the case and the post-redirection URL is provided.
This CL fixes that.

BUG= 922365 

Change-Id: Ic9acf354ef66d654ab41259aa0af297a56e775ce
Reviewed-on: https://chromium-review.googlesource.com/c/1411929
Commit-Queue: Yoav Weiss <yoavweiss@chromium.org>
Reviewed-by: Nicolás Peña Moreno <npm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#623293}
[modify] https://crrev.com/5ba90c2f9ee6e23c0ff0b22bc4ef0ae9477c57ad/third_party/blink/renderer/core/loader/threadable_loader.cc
[modify] https://crrev.com/5ba90c2f9ee6e23c0ff0b22bc4ef0ae9477c57ad/third_party/blink/renderer/platform/loader/fetch/resource_fetcher.cc
[modify] https://crrev.com/5ba90c2f9ee6e23c0ff0b22bc4ef0ae9477c57ad/third_party/blink/renderer/platform/loader/fetch/resource_request.cc
[modify] https://crrev.com/5ba90c2f9ee6e23c0ff0b22bc4ef0ae9477c57ad/third_party/blink/renderer/platform/loader/fetch/resource_request.h
[rename] https://crrev.com/5ba90c2f9ee6e23c0ff0b22bc4ef0ae9477c57ad/third_party/blink/web_tests/external/wpt/resource-timing/redirects.sub.html
[add] https://crrev.com/5ba90c2f9ee6e23c0ff0b22bc4ef0ae9477c57ad/third_party/blink/web_tests/external/wpt/resource-timing/resources/blank_page_green.htm.headers

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/9dc341fd7d70ef121bec311a1b7eaa1dce5828c0

commit 9dc341fd7d70ef121bec311a1b7eaa1dce5828c0
Author: Yoav Weiss <yoavweiss@chromium.org>
Date: Thu Jan 17 11:04:47 2019

Renamed ResourceRequest::OriginalUrl to InitialUrlForResourceTiming

Following feedback on [1], this is renaming OriginalUrl and commenting
it, to make it clear that it's a temporary stop-gap that should not be
used beyond the scope of ResourceTiming and should be removed once
Out-of-Blink CORS is shipped.

[1] https://chromium-review.googlesource.com/c/chromium/src/+/1411929

Bug:  922365 
Change-Id: I0bac3a13a4e765270cb911eaa1ab728bdd369d90
Reviewed-on: https://chromium-review.googlesource.com/c/1415261
Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Commit-Queue: Yoav Weiss <yoavweiss@chromium.org>
Cr-Commit-Position: refs/heads/master@{#623641}
[modify] https://crrev.com/9dc341fd7d70ef121bec311a1b7eaa1dce5828c0/third_party/blink/renderer/core/loader/threadable_loader.cc
[modify] https://crrev.com/9dc341fd7d70ef121bec311a1b7eaa1dce5828c0/third_party/blink/renderer/platform/loader/fetch/resource_fetcher.cc
[modify] https://crrev.com/9dc341fd7d70ef121bec311a1b7eaa1dce5828c0/third_party/blink/renderer/platform/loader/fetch/resource_request.cc
[modify] https://crrev.com/9dc341fd7d70ef121bec311a1b7eaa1dce5828c0/third_party/blink/renderer/platform/loader/fetch/resource_request.h