Track whether notification permission requests are made at the top-level.

Track whether notification permission requests are made at the top-level.

This patch adds a histogram tracking whether the requesting and the
embedding origin are different when requesting permission to display
Web Notifications. Notifications currently don't have this requirement,
but it would be great if we can introduce it.

BUG=416894
Committed: https://crrev.com/1398c49250282871b85fdfb0ea8dd00c13f6ae81
Cr-Commit-Position: refs/heads/master@{#316838}

[Peter Beverloo, 2015-02-18 11:46:38]

peter@chromium.org changed reviewers:
+ asvitkine@chromium.org

[Peter Beverloo, 2015-02-18 11:46:38]

+asvitkine for histogram addition

[mlamouri (slow - plz ping), 2015-02-18 11:53:00]

mlamouri@chromium.org changed reviewers:
+ mlamouri@chromium.org

[mlamouri (slow - plz ping), 2015-02-18 11:53:00]

lgtm

[Alexei Svitkine (slow), 2015-02-18 15:26:05]

lgtm

[Peter Beverloo, 2015-02-18 15:42:31]

The CQ bit was checked by peter@chromium.org

[commit-bot: I haz the power, 2015-02-18 15:43:34]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/927433003/1

[commit-bot: I haz the power, 2015-02-18 16:26:07]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-18 16:27:16]

Patchset 1 (id:??) landed as
https://crrev.com/1398c49250282871b85fdfb0ea8dd00c13f6ae81
Cr-Commit-Position: refs/heads/master@{#316838}