For chip with input box, the input is not usable when there're a lot of chips, and zoom to 500%

[tinayuangao]

Bug, feature request, or proposal:

Bug

What is the expected behavior?

Chip list input box still usable with lots of chips & zoom to 500%

What is the current behavior?

User cannot input anything if there're a lot of chips and zoom to 500%

What are the steps to reproduce?

In input box of chip list, enter a lot of chips and zoom to 500%

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Plunker template: https://goo.gl/DlHd6U

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?

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