GitLab

Adds crosapi GetHistograms to allow ash pull the lacros histograms
from lacros and attach it in the unified feedback report as
a zipped file lacros_histograms.zip.

TEST:
1. Start Lacros chrome, send a feedback report. Verify on listnr
that the feedback report contains lacros_histograms.zip. Download
and unzip the file and verify the histogram data in unzipped file
looks good.
2. Don't launch Lacros chrome, send a feedback report from ash.
Verify on listnr that the feedback report does not contain
lacros_histograms.zip.

Bug: 1119925
Change-Id: I91f5f05270d28ec038fcb5f9ea5002191ebd7f5e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2493363Reviewed-by: Miriam Zimmerman <mutexlox@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Reviewed-by: Greg Kerr <kerrnel@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Commit-Queue: Jenny Zhang <jennyz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#821054}