md-select label and placeholder remains visible even if container is set to hidden

[ffredsh]

Bug, feature request, or proposal:

Bug

What is the expected behavior?

When setting 's visibility to hidden, the label and placeholder should be hidden.

What is the current behavior?

Placeholder and label remains visible even if md-select is set to hidden.

What are the steps to reproduce?

https://plnkr.co/edit/TSvAYJ0grLr9gfR8rKxV?p=preview

1). Press "Toggle Select Visibility"
2). Notice that the placeholder is still visible and can be interacted with.

1). Select a value
2). Toggle visibility
3). Label still remains visible.

What is the use-case or motivation for changing an existing behavior?

I use md-select in a form and hide it when making an API request. The labels remain in place and does not look good.

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

Angular: 4.0.2
Material: 2.0.0-beta.3
OS: Ubuntu 14.04
Browser: Chrome

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