Currently there's no way to configure mus::Window and NativeWidgetMus via InitParams. One has to create the mus::Window and then views::NativeWidgetMus by hand before calling Widget::Init(). E.g. see https://code.google.com/p/chromium/codesearch#chromium/src/mash/login/login.cc&l=56

This seems like a pretty common thing to do, and it would be nice to centralize this code in one place. We could create a default implementation of NativeWidgetFactory on the ViewsDelegate in views::AuraInit, which would use the Mus Window properties passed with InitParams, and create the mus::Window and views::NativeWidgetMus based on those. 

The properties set in InitParams can be std::map<std::string, std::vector<uint8_t>> - i.e. the same type as what is passed to WindowManagerConnection::NewWindow(). 

Note sys_ui aslready does something similar (see NativeWidgetFactory::InitNativeWidget()), except it constructs the properties itself, but it probably makes sense to do this in all Mus clients.