MdSelect Performance Issues

#### Bug, feature request, or proposal:
On relatively slower devices (tested on Nexus 4), when we open Select list, select a value and close list the scrolling of page doesn't stays smooth.

#### What is the expected behavior?
Interaction with material component shouldn't create any side effect.

#### What is the current behavior?
Page scroll with jerkiness, after closing a select list with approx 100 list items.

在较慢的设备上打开并关闭一个包含约 100 个项目的选择列表，以重现该问题，然后检查 Angular Material MdSelect 的实现及其滚动行为。完成标准是：列表关闭后页面滚动仍然流畅，且不会引入交互副作用。

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