Repro steps:
1) Load dev Media Router extension
2) Open incognito tab
3) Cast tab

Expected: it works.
Actual: it fails to cast.

The reason is that chrome.tabs.get() fails to find the given tab because the dev extension does not have proper permissions to for the chrome.tabs API implementation to include incognito tabs in the search.

I did some digging and found that "include incognito" is guarded by the "whitelisted_for_incognito" feature. The whitelist is defined in extensions/common/api/_behavior_features.json, and once I added an entry for Media Router dev extension and remove the "location": "external_component" entry, it works.

Devlin: Would you be ok with making the modification mentioned above, or is there another workaround available?