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This Cl removes unused headers for TabModel use and cleans the gn files.

Bug: 1045575, 1050138, 1049845
Change-Id: I05dd5a083d15f70642a49541f2b80bc238db18dd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2144967Reviewed-by: Mark Cogan <marq@chromium.org>
Commit-Queue: Nazerke Kalidolda <nazerke@google.com>
Cr-Commit-Position: refs/heads/master@{#758802}