Computer Configuration > Administrative Templates > Google Chrome > Google Cast
Both
HKLM\Software\Policies\Google\Chrome
Setting the policy to Enabled displays the Cast toolbar icon on the toolbar or the overflow menu, and users can't remove it. Setting the policy to Disabled or leaving it unset lets users pin or remove the icon through its contextual menu. If the policy EnableMediaRouter is set to Disabled, then this policy's value has no effect, and the toolbar icon doesn't appear.