Bug, feature request, or proposal:

Proposal

What is the expected behavior?

Allow for a properly-sized and positioned progress spinner to be triggered inside a mat-button, temporarily overriding its initial content

What is the current behavior?

No configuration available, can manually place and position a progress spinner inside a mat-button

What are the steps to reproduce?

This is a sample template thrown together (very unoptimized): https://stackblitz.com/edit/angular-material2-issue-qbjrmi?file=app%2Fapp.component.html

Click on LOADING to trigger the spinner

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

Defined in the spec: https://material.io/design/components/progress-indicators.html#circular-progress-indicators under “Integrating with actions”

Is there anything else we should know?

Probably needs an a11y review since the content of the button will change