feat: add events for spellcheck dictionary downloads (#22556)

Co-authored-by: Samuel Attard <sattard@slack-corp.com>

docs/api/session.md

@@ -105,6 +105,45 @@ Returns:
 Emitted when a render process requests preconnection to a URL, generally due to
 a [resource hint](https://w3c.github.io/resource-hints/).
 
+#### Event: 'spellcheck-dictionary-initialized'
+
+Returns:
+
+* `event` Event
+* `languageCode` String - The language code of the dictionary file
+
+Emitted when a hunspell dictionary file has been successfully initialized. This
+occurs after the file has been downloaded.
+
+#### Event: 'spellcheck-dictionary-download-begin'
+
+Returns:
+
+* `event` Event
+* `languageCode` String - The language code of the dictionary file
+
+Emitted when a hunspell dictionary file starts downloading
+
+#### Event: 'spellcheck-dictionary-download-success'
+
+Returns:
+
+* `event` Event
+* `languageCode` String - The language code of the dictionary file
+
+Emitted when a hunspell dictionary file has been successfully downloaded
+
+#### Event: 'spellcheck-dictionary-download-failure'
+
+Returns:
+
+* `event` Event
+* `languageCode` String - The language code of the dictionary file
+
+Emitted when a hunspell dictionary file download fails.  For details
+on the failure you should collect a netlog and inspect the download
+request.
+
 ### Instance Methods
 
 The following methods are available on instances of `Session`: