This is on Chrome M70 with the Harmony UI.

What steps will reproduce the problem?
(1) Change the source to "Cast desktop".
(2) Select a Chromecast device.
(3) An OS system dialog appears prompting the user to confirm sharing the contents of their screen by selecting "Share" or "Cancel".
(4) Click "Cancel".

What is the expected result? I just think it's odd to show "Failed to cast. Please try again." In this particular case, there might be some more relevant wording, or perhaps no message at all? I guess this is more my feedback than a bug (So I marked this as a feature request).

What happens instead? The Cast icon changes to its error state (orange with exclamation mark), and the user is presented with a a "failed to cast. Please try again." msg under the target cast device in the dialog.