[Sidenav] Issue when container and sidenav in different components

#### Bug, feature request, or proposal:
I have the template like this:
``
` `
`...`
``

`` is:
``
` ...`
``

When I have my sidenav in two components like this, the mode "**side**" is not working anymore. The mode switch to "**over**".
When I have all in the same component, it's working.

I think it's due to a another tag between and and it break the css rules.

#### Which versions of Angular, Material, OS, TypeScript, browsers are affected?
Angular Material 5.0.1

Comience reproduciendo la plantilla indicada con Angular Material 5.0.1, colocando mat-sidenav-container y mat-sidenav en componentes separados, y compárela después con la disposición en el mismo componente. Se considera terminado cuando mode="side" sigue siendo efectivo al anidar la sidenav en my-component en lugar de cambiar a mode="over".

Escrito por el modelo de indexación a partir del texto del issue.