We have been firing the PermissionDeniedError exception from the start, are we completely confident it's fine to change this? A quick search on Google and GitHub tell me it probably is— the only references I can find are the Gecko and Blink tests, but maybe Mat/Matt knows about other usage?

I'm not aware of anyone relying on this, although as with any change I'm sure some people will get broken, but if all browsers are going to implment this, change sooner rather than later is better. I'm assuming this change is to make the error throwable based on different issues rather than just when the user denies the permission? If not, why change, because this error is harder to understand at first glance.

I think mlamouri added it for a non-permission related case in the presentation api.

Mozilla uses a NotAllowedError as well now, so let's match the spec.

[1] https://github.com/mozilla/gecko-dev/blob/cb4337c62c0b60b93d118e7cb5b769a2a2386703/dom/base/domerr.msg#L156

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/bd3b430d88ca5ffb6544c0283cdf6a65489eede2

commit bd3b430d88ca5ffb6544c0283cdf6a65489eede2
Author: peter <peter@chromium.org>
Date: Thu Aug 04 12:23:59 2016

Use NotAllowedError instead of PermissionDeniedError for the Push API

BUG= 611340 

Review-Url: https://codereview.chromium.org/2199213003
Cr-Commit-Position: refs/heads/master@{#409766}

[modify] https://crrev.com/bd3b430d88ca5ffb6544c0283cdf6a65489eede2/chrome/browser/push_messaging/push_messaging_browsertest.cc
[modify] https://crrev.com/bd3b430d88ca5ffb6544c0283cdf6a65489eede2/content/child/push_messaging/push_provider.cc
[modify] https://crrev.com/bd3b430d88ca5ffb6544c0283cdf6a65489eede2/content/renderer/push_messaging/push_messaging_dispatcher.cc
[modify] https://crrev.com/bd3b430d88ca5ffb6544c0283cdf6a65489eede2/third_party/WebKit/LayoutTests/http/tests/push_messaging/subscribe-failure-permission-denied-in-document.html
[modify] https://crrev.com/bd3b430d88ca5ffb6544c0283cdf6a65489eede2/third_party/WebKit/Source/modules/push_messaging/PushError.cpp
[modify] https://crrev.com/bd3b430d88ca5ffb6544c0283cdf6a65489eede2/third_party/WebKit/public/platform/modules/push_messaging/WebPushError.h