[Tooltip] Change detection runs after showing tooltip

#### Bug, feature request, or proposal:

Bug

#### What is the expected behavior?

Hovering an element with a `matTooltip` should not trigger change detection on this element if it is an `OnPush` element and its `@Input()`s does not change.

#### What is the current behavior?

Hovering an element with a `matTooltip` triggers change detection on this element.

This only happens if `matTooltip` is defined using `[matTooltip]="..."` and not when it is defined using `matTooltip="..."`

#### What are the steps to reproduce?

See https://stackblitz.com/edit/angular-material2-issue-ocg9sj
- pass the mouse on the red `div`
- you get logs everytime the function needed to draw the component are called
- you don't get any log from `ngOnChanges`
- I would expect that since the `@Input()` didn't change, the component shouldn't be redraw!

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

Prevent useless redraws

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

cf stackblitz

#### Is there anything else we should know?

リンクされた StackBlitz の再現から始め、OnPush 要素で値が [matTooltip] によってバインドされているときの matTooltip の動作を調べます。静的な matTooltip="..." のケースと比較し、ホバー中の change detection のログを確認します。@Input() の値が変更されていない場合に、ホバーによって不要な change detection が発生しなければ完了です。

索引モデルが issue の本文から書いたものです。