Findit identified the culprit r583407 with confidence 70.0% in the config "chromium.linux / Linux Tests (dbg)(1)(32)"
based on the flakiness trend:

https://findit-for-me.appspot.com/waterfall/flake?key=ag9zfmZpbmRpdC1mb3ItbWVy1wELEhdNYXN0ZXJGbGFrZUFuYWx5c2lzUm9vdCKgAWNocm9taXVtLmxpbnV4L0xpbnV4IFRlc3RzIChkYmcpKDEpKDMyKS81MjEwMC9icm93c2VyX3Rlc3RzL1UyRm1aVUp5YjNkemFXNW5UbVYwZDI5eWEwTnZiblJsZUhRdlRtVjBkMjl5YTBOdmJuUmxlSFJEYjI1bWFXZDFjbUYwYVc5dVFuSnZkM05sY2xSbGMzUXVRMkZqYUdVdk1nPT0MCxITTWFzdGVyRmxha2VBbmFseXNpcxgBDA

If the culprit above is wrong, please file a bug using this link and hit submit:
https://bugs.chromium.org/p/chromium/issues/entry?status=Unconfirmed&labels=Pri-1,Test-Findit-Wrong&components=Tools%3ETest%3EFindit%3EFlakiness&summary=%5BFindit%5D%20Flake%20Analyzer%20-%20Wrong%20result%20for%20SafeBrowsingNetworkContext/NetworkContextConfigurationBrowserTest.Cache/2&comment=Link%20to%20Analysis%3A%20https://findit-for-me.appspot.com/waterfall/flake?key=ag9zfmZpbmRpdC1mb3ItbWVy1wELEhdNYXN0ZXJGbGFrZUFuYWx5c2lzUm9vdCKgAWNocm9taXVtLmxpbnV4L0xpbnV4IFRlc3RzIChkYmcpKDEpKDMyKS81MjEwMC9icm93c2VyX3Rlc3RzL1UyRm1aVUp5YjNkemFXNW5UbVYwZDI5eWEwTnZiblJsZUhRdlRtVjBkMjl5YTBOdmJuUmxlSFJEYjI1bWFXZDFjbUYwYVc5dVFuSnZkM05sY2xSbGMzUXVRMkZqYUdVdk1nPT0MCxITTWFzdGVyRmxha2VBbmFseXNpcxgBDA

Automatically posted by the findit-for-me app (https://goo.gl/Ot9f7N).

Suspected CL speculatively reverted: https://chromium-review.googlesource.com/c/chromium/src/+/1177501

 Issue 874762  has been merged into this issue.

That seems to have done the trick. First successful build in a while:
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Linux%20Tests%20%28dbg%29%281%29%2832%29/52108

 Issue 874812  has been merged into this issue.

 Issue 874818  has been merged into this issue.

Fixed with https://chromium-review.googlesource.com/c/chromium/src/+/1178341.