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* Remove the two optionals BrowserTabMetadata from BrowserTabsModel.
* Adds sorted vector of BrowserTabMetadata to BrowserTabsModel, from
  most recently visited to least recently visited browser tabs.
* Modifies chrome://multidevice-internals to accommodate.

https://screenshot.googleplex.com/ASLmNrodybKchY6
https://screenshot.googleplex.com/5CyAkSuWD5wXM9g

Bug: 1106937
Change-Id: I5bc898b12db304491cec8091c51a2bf7b1c2ad24
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2415537
Commit-Queue: Regan Hsu <hsuregan@chromium.org>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#808108}