[Feed] Add histograms for different behaviors when scheduler refresh

Add histograms for different behaviors when scheduler refresh to easy
understand why scheduler returns kNoRequestWithWait so often.

Bug: 931265
Change-Id: I59f5a08f262b1c11c152790d442bb6c900c3045b
Reviewed-on: https://chromium-review.googlesource.com/c/1471391
Commit-Queue: Gang Wu <gangwu@chromium.org>
Reviewed-by: Brian White <bcwhite@chromium.org>
Reviewed-by: Sky Malice <skym@chromium.org>
Cr-Commit-Position: refs/heads/master@{#632686}
4 files changed