Add UserCounter for Top Navigation in sandbox

Add UserCounter for Top Navigation in sandbox

To tell us the % of page views that do top navigations in sandboxed
iframes w/ or w/o 'allow-top-navigation' and user gesture.

This is for this intent to implement/ship feature:
https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/Flt2IixYQK4

BUG=662506
Review-Url: https://codereview.chromium.org/2614073004
Cr-Commit-Position: refs/heads/master@{#442072}
(cherry picked from commit 3180362167493d3261e31d0cb4a7fa1f5180683f)

Review-Url: https://codereview.chromium.org/2621043002 .
Cr-Commit-Position: refs/branch-heads/2924@{#715}
Cr-Branched-From: 3a87aecc31cd1ffe751dd72c04e5a96a1fc8108a-refs/heads/master@{#433059}
Committed: https://chromium.googlesource.com/chromium/src/+/5f34cba74251583df913a4fdd8fd0f4529c96adf

[gogerald1, 2017-01-10 16:23:26]

Description was changed from

==========
Add UserCounter for Top Navigation in sandbox

To tell us the % of page views that do top navigations in sandboxed
iframes w/ or w/o 'allow-top-navigation' and user gesture.

This is for this intent to implement/ship feature:
https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/Flt2IixYQK4

BUG=662506

Review-Url: https://codereview.chromium.org/2614073004
Cr-Commit-Position: refs/heads/master@{#442072}
(cherry picked from commit 3180362167493d3261e31d0cb4a7fa1f5180683f)
==========

to

==========
Add UserCounter for Top Navigation in sandbox

To tell us the % of page views that do top navigations in sandboxed
iframes w/ or w/o 'allow-top-navigation' and user gesture.

This is for this intent to implement/ship feature:
https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/Flt2IixYQK4

BUG=662506

Review-Url: https://codereview.chromium.org/2614073004
Cr-Commit-Position: refs/heads/master@{#442072}
(cherry picked from commit 3180362167493d3261e31d0cb4a7fa1f5180683f)

Review-Url: https://codereview.chromium.org/2621043002 .
Cr-Commit-Position: refs/branch-heads/2924@{#715}
Cr-Branched-From:
3a87aecc31cd1ffe751dd72c04e5a96a1fc8108a-refs/heads/master@{#433059}
Committed:
https://chromium.googlesource.com/chromium/src/+/5f34cba74251583df913a4fdd8fd...
==========

[gogerald1, 2017-01-10 16:23:27]

Committed patchset #1 (id:1) manually as
5f34cba74251583df913a4fdd8fd0f4529c96adf.