7d758be5d2
When an extension's content script is very slow and causes a webpage to hang noticeably, a warning banner is displayed to the user. It would be useful to also notify the extension developer when that happens, so that they can address the issue. Let's add a new event runtime.onPerformanceWarning that can be dispatched when the browser needs to warn an extension of runtime performance issues. For now, let's just dispatch that event when the slow extension warning banner is displayed to the user. See also https://github.com/w3c/webextensions/issues/456 Differential Revision: https://phabricator.services.mozilla.com/D194708