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This CL fixes :
1 - Fixed layout styling for section header
2 - Added plumbing to mark an article as read
3 - Added fix to show the sign-in promo at the top of reading list
4 - Fixed search state to not show any read/unread section headers

Bug: 1148472, 1148524
Change-Id: I6269b28bf7146acc684437446686c76c88006892
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2535616Reviewed-by: Theresa  <twellington@chromium.org>
Commit-Queue: Shakti Sahu <shaktisahu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#827135}