GitLab

This metric will help to diagnose possible URL spoofing bugs in Slim
Navigation feature. _documentURL is used as proxy for legacy navigation
manager URL, which is generally reliable and almost always match
last committed URL.

Collection review doc:
https://docs.google.com/document/d/14SygQ8BzLkzedTLuDfOHhakQHZOOJSU8TAJT3rxBGv4/edit#

Bug: 1182320
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I6dcf5711f0fd42063b67afb0fa0a99b77ce4c7a0
Reviewed-on: https://chromium-review.googlesource.com/1187014
Commit-Queue: Eugene But <eugenebut@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Cr-Commit-Position: refs/heads/master@{#586110}