[MatSidenav] Sidenav Toggling Can Cause Content Shifting

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

#### What is the expected behavior?
Mat-sidenav-content is not moved from original position upon quick mat-sidenav toggles

#### What is the current behavior?
Quick mat-sidenav toggles can cause mat-sidenav-content to be shifted over until the drawer is toggled again

#### What are the steps to reproduce?

Set the autofocus on mat-sidenav to true, and place a focusable input in the mat-sidenav
Click the 'open drawer' button quickly and repeatedly until the content shifts. Click the button again and the content will shift back.

https://stackblitz.com/edit/angular-eesonu

#### What is the use-case or motivation for changing an existing behavior?
Use-case: User accidentally opens the drawer and quickly presses again to undo the action. This will result in possibly all content on the page not being displayed.

#### Which versions of Angular, Material, OS, TypeScript, browsers are affected?
Angular: 6.0.9
Material: 6.4.1

まず、autofocus を有効にし、MatSidenav 内にフォーカス可能な input を配置した状態で、リンク先の StackBlitz の動作を再現します。次に、素早く切り替えたときの MatSidenav と mat-sidenav-content の動作を調べます。繰り返し開閉しても mat-sidenav-content がずれたままにならず、位置を戻すためにその後の切り替えが必要なくなれば完了です。

索引モデルが issue の本文から書いたものです。