Re-add DCHECKS now that the referenced bug is fixed

It's green now. (*)

(*) https://ci.chromium.org/ui/test/chromium%3Aci/ninja%3A%2F%2F%3Ablink_web_tests%2Fvirtual%2Fthreaded%2Fhttp%2Ftests%2Fdevtools%2Ftracing%2Fgeneric-trace.js?q=VHASH%3A3801f7574b4dfa26

Bug: 1446721

Change-Id: I02f8a3af2c3926df87af22abf71314b705c23242
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4583352


Reviewed-by: Aaron Leventhal <aleventhal@chromium.org>
Commit-Queue: Aaron Leventhal <aleventhal@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1152639}