[Feed Internals] Add FeedProcessScope dump

This internals page is used to surface debugging information useful to
developers of the NTP Interest Feed.

Add button to get internal information about the FeedProcessScope state
as a formatted string.

https://screenshot.googleplex.com/z4Sv9axqgYa

Bug: 940707
Change-Id: I4e2893e17affb83b2784b9ed785042419c11943b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1516874
Reviewed-by: Will Harris <[email protected]>
Reviewed-by: Sky Malice <[email protected]>
Commit-Queue: Natalie Chouinard <[email protected]>
Cr-Commit-Position: refs/heads/master@{#639971}
9 files changed