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behind the fullscreen and profile buttons.
Calculate the maximum number of times we can show and hide the rest, similar
to how it works on Linux and Windows.
Also changed so that only the one active tab has a bigger minimum width (and
draws the close button) instead of potentially multiple selected tabs. This also
matches Linux and Windows.

BUG=392137

Review URL: https://codereview.chromium.org/476313003

Cr-Commit-Position: refs/heads/master@{#293654}