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Changed BuildWindowListIgnoreModal to keep the activation order.
This also fixes the method not to add a window w/o parent.

Bug: None
Test: covered by unittests.
Change-Id: I727b3af0421b9f0f61552ec4a25e440e30e903d7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1935287
Commit-Queue: Mitsuru Oshima <oshima@chromium.org>
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#720767}