Oystein, have you already started this?

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/ef24a291c6ecdac0f3fc509304e3a128268bfcba

commit ef24a291c6ecdac0f3fc509304e3a128268bfcba
Author: Steven Holte <holte@google.com>
Date: Fri Aug 04 23:59:08 2017

Add unique NavigationIDs to NavigationHandles.

This allows UKM logs to have a unambiguous way of referring to a
particular navigation.

PageLoadTracker is modified to start using them.

Bug:  705741 
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_site_isolation
Change-Id: Ib1c57d3d37cba55b207912480b9a0f44f3846074
Reviewed-on: https://chromium-review.googlesource.com/580586
Reviewed-by: Camille Lamy <clamy@chromium.org>
Reviewed-by: Charlie Reis <creis@chromium.org>
Reviewed-by: Bryan McQuade <bmcquade@chromium.org>
Reviewed-by: Oystein Eftevaag <oysteine@chromium.org>
Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Commit-Queue: Steven Holte <holte@chromium.org>
Cr-Commit-Position: refs/heads/master@{#492185}
[modify] https://crrev.com/ef24a291c6ecdac0f3fc509304e3a128268bfcba/chrome/browser/page_load_metrics/page_load_tracker.cc
[modify] https://crrev.com/ef24a291c6ecdac0f3fc509304e3a128268bfcba/content/browser/frame_host/navigation_handle_impl.cc
[modify] https://crrev.com/ef24a291c6ecdac0f3fc509304e3a128268bfcba/content/browser/frame_host/navigation_handle_impl.h
[modify] https://crrev.com/ef24a291c6ecdac0f3fc509304e3a128268bfcba/content/public/browser/navigation_handle.h

Steve, is there anything else to be done here or can this be closed?

I think all of the work here is complete since we have Navigation IDs on all platforms.