When adding a new chip in chip list, the screen reader read "chip deleted"

[tinayuangao]

Bug, feature request, or proposal:

Bug

What is the expected behavior?

The screen reader should read something like "chip added"

What is the current behavior?

If chip "chip" is added, it reads "chip deleted"

What are the steps to reproduce?

In input box of chip list, enter "chip" and hit enter.

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

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

Is there anything else we should know?

[tinayuangao]

Fixed by #6706

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