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This CL includes the following:
- data plumbing for the collapsed boolean
- logic for showing collapsed based on the flag
- updating the tab bounds if collapsed

Change-Id: Iadcba24738eab795945134a8b77b98076fe59491
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2159931
Commit-Queue: Charlene Yan <cyan@chromium.org>
Reviewed-by: Connie Wan <connily@chromium.org>
Cr-Commit-Position: refs/heads/master@{#769063}