[Dev UI] Image rendering within JSON objects

[shrutip90]

Displaying base64 encoded images from media response from a flow shows "undefined":

same media part deeper down in the trace (model response) renders fine:

Also see https://screencast.googleplex.com/cast/NTM3NzI4MzE1NzEzMTI2NHw4NDYzNjVlYS04YQ