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As part of Feed development, add entry points to allow an XSurface
client to open a page in a new tab, open in an incognito tab, or
download the URL as an offline page.

Bug: 1099057
Change-Id: Id6152147c105993d88aa08cee9f16ea42da45b2d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2265497Reviewed-by: Dan H <harringtond@chromium.org>
Reviewed-by: Justin DeWitt <dewittj@chromium.org>
Reviewed-by: Jian Li <jianli@chromium.org>
Commit-Queue: Peter Williamson <petewil@chromium.org>
Cr-Commit-Position: refs/heads/master@{#782741}