Roughly 2 years ago we coalesced these two settings, so that the user just answered one prompt for both notifications and push notifications. The PUSH_MESSAGING content setting is now only used in the following circumstance:
If it has previously been disabled for a given origin, that origin will not have access to push notifications.
However, the PUSH_MESSAGING content setting will never be set by any current code in Chrome.
There are several issues with the PUSH_MESSAGING content setting:
There is no way for a user to view or change existing settings to CONTENT_SETTINGS_TYPE_PUSH_MESSAGING. This has privacy consequences.
It is very hard/impossible for a user to reason about how their PUSH_MESSAGING content setting has an impact on them, if it is set.
Keeping this content setting increases the complexity of the code and is a maintenance burden.
Comment 1 by bugdroid1@chromium.org
, Jul 19 2016