Dismissing a workbench message doesn't wrap up API promise

[joaomoreno]

Testing #5743

The promise returned by vscode.window.showInformationMessage() never completes if the user dismisses it with Escape.

I expected it to complete with undefined, similarly to when pressing Close.

[jrieken]

Good find. @bpasero How do I find out when dispose by Esc happens?

[bpasero]

@jrieken hm, not so straight forward but I can see two possible options with the existing way it works:

• I seem to dispose the actions of messages when they get hidden so you could detect that in your action (e.g. the close action if you have one) and know that the message hides
• there is an event onMessagesCleared that gets fired after all messages get cleared (https://github.com/Microsoft/vscode/blob/master/src/vs/workbench/services/message/browser/messageService.ts#L55). this event is currently not exposed on IMessageService but we could add it there

[jrieken]

I can go with option #1