The MR toolbar icon should have "Hide in Chrome menu" / "Show in toolbar" options in the context menu, like normal extension icons.

The option should be disabled when the icon is ephemeral (once the ephemeral icon [1] lands), because when the icon is ephemeral, its position doesn't get saved.

Related: b/30081884

[1] https://bugs.chromium.org/p/chromium/issues/detail?id=594577