aria-multiline attribute on Autocomplete

[vertigo7x]

Bug, feature request, or proposal:

Bug

What is the expected behavior?

Pass wai-aria validation using Axe

What is the current behavior?

The autocomplete component have an input with an attribute aria-multiline set to false, but the specification wai-aria-1.1 says that the child element should have the aria-multiline attribute:

A composite widget containing a single-line textbox and another element, such as a listbox or grid, that can dynamically pop up to help the user set the value of the textbox.
Authors must ensure an element with role combobox contains or owns a text input element with role textbox or searchbox and that the text input has aria-multiline set to false. If the combobox provides autocompletion behavior for the text input as described in aria-autocomplete, authors must set aria-autocomplete on the textbox element to the value that corresponds to the provided behavior.

What are the steps to reproduce?

Pass accessibility validation using Axe for Chrome on Autocomplete

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

material 2.0.0-beta.10

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