Dialogue - overflow scrolling on small screens and margins

#### Bug, feature request, or proposal:
The current dialogue does not seem to support sizing and scrolling on smaller screen sizes / small devices. This was possible on the material 1 dialogue. If the vertical height of the screen was incredibly small scrollbars would appear see this screenshot:


With version 2 - the dialogue is pushed off the screen and no scrollbars ever appear in the middle. It does not maintain any margins on the top or bottom.


Maybe there is this a means this can be achieved but the examples are quite primitive.

#### What is the expected behavior?
When screen is decreased in size scrollbars should appear for the content.

#### What is the current behavior?
The current dialogue is pushed off the screen with no margin at the top or bottom. The content remains the same size

#### What are the steps to reproduce?

Providing a Plunker (or similar) is the *best* way to get the team to see your issue.
https://plnkr.co/edit/DrI42Su0v6OntJkjUNOI?p=preview

#### What is the use-case or motivation for changing an existing behavior?
The current modal is only useful for very simple use cases.

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

#### Is there anything else we should know?

Commencez par la reproduction liée dans Plunker et examinez le comportement de la boîte de dialogue Angular Material lorsque la hauteur du viewport est réduite. Comparez la version actuelle avec le comportement de Material 1 décrit, en vous concentrant sur les marges verticales et le débordement du contenu. C’est terminé lorsque la boîte de dialogue reste dans le viewport et que son contenu devient défilable lorsque l’écran est trop petit.

Rédigé par le modèle d'indexation à partir du texte de l'issue.