Components: [md-radio] required attribute doesn't work for md-radio-group or md-radio-button

[chase0213]

Bug, feature request, or proposal:

bug, (or feature request)

What is the expected behavior?

required attribute is available in md-radio-group or md-radio-button,
i.e., when a user clicks submit button in a form without selecting any required radio options,
the form should tell the user that (s)he needs to select one of those.

refs. w3c description about "input required"
https://www.w3.org/TR/html5/forms.html#attr-input-required

What is the current behavior?

required attribute is ignored without any errors or warnings.

What are the steps to reproduce?

Visit the following plunker page:
http://plnkr.co/edit/6Y2L1cLwYX2TOXv5UDOu?p=preview

In the plunker, we have 2 forms, one with naive html5 radio buttons and the other with md-radio-group and md-radio-buttons.
In the upper form, we cannot 'save' without selecting any options,
but in the lower one, it seems we can 'save' without selecting anything.

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

Client side validation same as md-input or naive input type='radio'.

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

angular: 2.0.2
material: 2.0.0-alpha.9-3
os: OSX El Capitan 10.11.6
browser: Google Chrome 54.0.2840.71 (64-bit)

Is there anything else we should know?

[csabattilas]

@jelbourn @kara Hello, do we intend to fix this. I started to work on this by adding the required property on the md-radio-group and automatically updating the required attribute on the md-radio-button. Is that ok? Should I create the PR?
thanks

[emreavsar]

is this still untouched? i'm very interested in that pr

[willshowell]

@emreavsar looks like @krigton put together a PR (https://github.com/angular/material2/pull/1690) that was approved but stalled for a few months and closed

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