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This CL adds the following actions to the ReadingList Context Menu:
- Mark As Read
- Mark As Unread
- View Offline Version in New Tab

Bug: 1093302
Change-Id: Ie17e58417738cbc5cc2c3a345c281464339170b5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2366799Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Reviewed-by: Sebastien Lalancette <seblalancette@chromium.org>
Commit-Queue: Ewann Pellé <ewannpv@chromium.org>
Cr-Commit-Position: refs/heads/master@{#803116}