Dialog action button are half hidden on mobile devices

#### Bug

#### What is the expected behavior?
The action buttons should be visible

#### What is the current behavior?
They are not fully visible

#### What are the steps to reproduce?
https://stackblitz.com/edit/angular-material2-issue-dialog-button
And scroll the lower console part up:

#### What is the use-case or motivation for changing an existing behavior?
User can't use the action button on small devices

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

#### Is there anything else we should know?
This is not the first issue I'm opening on the dialog, my last issue wasn't even answered. I hope this will be different...

Inizia con la riproduzione collegata di StackBlitz e testa il dialogo in un viewport mobile piccolo, incluso lo scorrimento verso l’alto dell’area inferiore della console. Verifica che i pulsanti di azione siano completamente visibili e utilizzabili; l’issue non indica alcun file del repository né alcun test da ispezionare.

Scritto dal modello di indicizzazione a partire dal testo della issue.