Exclude devtools: tab from primary window determination

When --auto-open-devtools-for-tabs command line switch is used with
Chromium, the resulting DevTools window can race against the page itself
in getting selected as the primary window. This CL excludes targets
prefixed with `devtools://` from primary window determination logic.
Also adds a regression test for crbug.com/427908560

Bug: 427908560
Change-Id: Id4e804cee4b38eb0679d1738c669c6be0068c905
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6769505
Reviewed-by: Mathias Bynens <mathias@chromium.org>
Commit-Queue: Alex N. Jose <alexnj@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1489507}