Progress spinner shakes when specifying a diameter.

#### Bug:

When specifying a diameter (16-32px) on the progress spinner the animation will eventually start to shake by a couple pixels as it animates. Using smaller diameters make it more noticeable. Using other components with animations (material inputs, etc.) makes it worse.

#### What is the expected behavior?

Progress spinner has a smooth animation that doesn't shake as it animates.

#### What is the current behavior?

Over time, the progress spinner will begin to shake up and down as it animates.

#### What are the steps to reproduce?

https://stackblitz.com/edit/angular-material2-issue-xg5xgq

1) Load the stackblitz demo
3) Click on the input (trigger the label animation)
4) Click away from the input (return it to normal)
5) Watch for the progress spinner to shake.
6) The progress spinner animation will never recover.

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

The issue appears worse the more material components are on the page. Currently, progress spinner is unusable in our app because the shaking is distracting and unpleasant.

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

Angular: 6.0.3
Material: 6.2.0
Chrome: Version 67.0.3396.79 (Official Build) (64-bit)

Bắt đầu với bản tái hiện StackBlitz được liên kết và kiểm tra triển khai của progress-spinner, tập trung vào animation dành riêng cho đường kính sau khi input label được kích hoạt. Xác nhận hiện tượng shake trong setup bị ảnh hưởng và kiểm tra rằng spinner 16–32px vẫn mượt sau khi input được focus rồi blur.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.