md-slide-toggle: has no focus indicator

[quanterion]

• Do you want to request a feature or report a bug?
  It is a bug
• What is the current behavior?
  md-slide-toggle has no focus indicator
• If the current behavior is a bug,
  please provide steps to reproduce and if possible a minimal demo of the problem

Just open a demo-app, go to Slide Toggle, click on the first slide toggle control and press Space key. The control should display focus indicator

• Which version of Angular and Material, and which browser and OS does this issue affect?
  Did this work in previous versions of Angular / Material?
  Please also test with the latest stable and snapshot versions.

I tested on Windows with Firefox and Chrome browsers
It works in Material1.

[jelbourn]

@devversion follow-up for your initial PR?

[devversion]

@jelbourn Yeah, definitely. Will work on that as soon as possible.

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