I believe there are two things that could be done here:

1. Make the first determination of "is it exported" based on the history of both repos, not by searching for GitHub PRs.
2. A mechanism to mark a problem like this as resolved, if it was resolved by squashing two commits or otherwise making it impossible for our tooling to match them.

Marking as dup: the immediate issue can be resolved by  bug 756202 .

Regarding the suggestions (they are great ideas!):

1. Searching for "exported" commits in git history is easy to implement and much more reliable than searching through PR description. However, we still need to comb through open PRs and closed-but-not-merged (abandoned for whatever reason) PRs. I will consider this when I refactor the whole "exportable" detection.
2. Perhaps once we have  bug 756202  implemented, we can simply create pseudo PRs that include change IDs in the description as a skip list.

Yep,  issue 756202  would fix this since https://github.com/w3c/web-platform-tests/pull/6822 mentions both Change-Ids. Although I didn't add the chromium-export label to it, I guess it won't be found?

If we move to using the git history as the primary means for "exportable" detection, I wonder how explicitly we should maintain the exceptions. (A similar list will be needed for issue 754619.) To close a PR in wpt is not a very explicit "let's revert this from Chromium" after all. But perhaps we could use PRs just like that, and then flag it in the audit script, which would only look at commit history. (Maintaining such a list day-to-day might be tedious.)

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a08870c2f65118997b021028f02a021c9a68d082

commit a08870c2f65118997b021028f02a021c9a68d082
Author: Charlie Andrews <charliea@chromium.org>
Date: Fri Sep 15 20:08:07 2017

Revert to an older version of the Google barackobama story

This story is failing on all bots since my update yesterday.

TBR=nednguyen@google.com

Bug:  756383 
Change-Id: I8ebec75c0123833dcead1750983a2790cab1bff9
Reviewed-on: https://chromium-review.googlesource.com/668685
Commit-Queue: Charlie Andrews <charliea@chromium.org>
Reviewed-by: Charlie Andrews <charliea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#502343}
[modify] https://crrev.com/a08870c2f65118997b021028f02a021c9a68d082/tools/perf/page_sets/data/top_25.json

The change above seems to be a typo. Please ignore.