[Tabs] background from :focus pseudoselector is visible until the next click anywhere

[rudzikdawid]

Bug, feature request, or proposal:

Bug: after change tab, background from :focus pseudoselector is visible until the next click (anywhere).

What is the expected behavior?

after change tab, background from :focus pseudoselector, should automatically disappear without extra click

What is the current behavior?

tab background from :focus pseudoselector is visible until the next click (anywhere).

What are the steps to reproduce?

1. open https://material.angular.io/components/tabs/examples
2. click in one of the tabs for change it
3. wait for tab change
4. after tab change: background from :focus pseudoselector is still visible
5. click anywhere to hide background from :focus pseudoselector

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

fix visual bug, improve UX

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

angular: 6.0.0
material: 6.0.0
Browser: Latest desktop Firefox/Chrome
OS: Fedora

Is there anything else we should know?

[angular-automatic-lock-bot]

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