Add a use counter for navigations targeted at _current

It's not in the spec, FF doesn't support it. Hopefully we can remove it.

Change-Id: Iaa9b78245d3513a2574570359f02922da09b5ed6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1536010
Commit-Queue: Dmitry Gozman <dgozman@chromium.org>
Auto-Submit: Nate Chapin <japhet@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#644132}
3 files changed