[Feed Internals] Add button to force Feed refresh

Add an action to trigger a force refresh of the Feed from the internals
debugging page, without clearing the cache.

Bug: 940675
Change-Id: Iaf28eba69a7f611f801a57948bc0e9da4d3f32a2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1531427
Reviewed-by: Ken Buchanan <kenrb@chromium.org>
Reviewed-by: Sky Malice <skym@chromium.org>
Commit-Queue: Natalie Chouinard <chouinard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#642721}
8 files changed