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This CL adds an API to TabSelectionEditorController that shows the
TabSelectionEditor with the given tabs, and the first n tabs being
selected. There is also a divider shows between the first n selected
tabs and the rest of the tabs.

Change-Id: I32aa764dc62bbabc89fe54641963b9f64274134e
Bug: 1004570
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1896866Reviewed-by: Wei-Yin Chen (陳威尹) <wychen@chromium.org>
Reviewed-by: Yusuf Ozuysal <yusufo@chromium.org>
Commit-Queue: Mei Liang <meiliang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#713897}