Bug 282436 – [WebDriver][BiDi] Support event subscription priority

• Component: WebDriver
• Status: NEW

[Lauro Moura]

https://w3c.github.io/webdriver-bidi/#event-subscribe-priority

The WebDriver BiDi spec allows events to have different subscription priorities. They define the order of the remote end steps (i.e. steps running on the browser) when multiple events are subscribed together.

> Optionally, a set of remote end subscribe steps, which define steps to take when a local end subscribes to an event. Where defined these steps have an associated subscribe priority which is an integer controlling the order in which the steps are run when multiple events are enabled at once, with lower integers indicating steps that run earlier.

Here are a few of the events that define the priority explicitly as of Nov 1st 2024:

* `browsingContext.contextCreated`, priority 1 - https://w3c.github.io/webdriver-bidi/#event-browsingContext-contextCreated
* `script.realmCreated`, priority 2 - https://w3c.github.io/webdriver-bidi/#event-script-realmCreated
* `log.entryAdded`, priority 10 - https://w3c.github.io/webdriver-bidi/#event-log-entryAdded

[Lauro Moura]

Adding dependency on bug271956 as it'll add the initial event support.

[Radar WebKit Bug Importer]

<rdar://problem/139510013>