<!--
  - Thanks for opening an issue for us!  Before you open an issue,
  - please check if a similar issue exists or has been closed before.
  -
  - If you're asking a question about how to use Blockly in your application,
  - please ask questions on the mailing list, instead of filing issues:
  -       https://groups.google.com/forum/#!forum/blockly
  -->

### Problem statement

<!-- TODO: Please describe the problem.
  -        Is it a bug report (something didn't work the way you expected),
  -        or a feature request (something new you think would improve Blockly)?
  -->

### Expected Behavior

<!-- TODO: Please describe what should happen.
  -        Include screenshots if applicable.
  -->

### Actual Behavior

<!--  TODO: Describe what actually happens.
  -         Include screenshots if applicable.
  -->

### Steps to Reproduce

<!-- TODO: Explain what someone needs to do in order to see
  -        what's described in *Actual behavior* above
  -->

1. Start by..
2. Next, do..

### Stack Traces

<!-- TODO: Please open up the console.  If you see any Blockly-related errors,
  -        paste them between the quotes below.
  -
  - Ignore any instances of...
  - "Uncaught (in promise) DOMException: The play() request was interrupted by a call to pause()."
  -->

```
Replace with error stack trace.
```

### Operating System and Browser

<!-- TODO: If this issue is browser specific, uncomment the systems you have tested. -->

<!-- * Desktop Chrome -->
<!-- * Desktop Firefox -->
<!-- * Desktop Safari -->
<!-- * Desktop Opera -->
<!-- * Windows Internet Explorer 10 -->
<!-- * Windows Internet Explorer 11 -->
<!-- * Windows Edge -->

<!--
* Smartphone/Tablet/Chromebook (please complete the following information):
  * Device: [e.g. iPhone6]
  * OS: [e.g. iOS8.1]
  * Browser [e.g. stock browser, safari]
  * Version [e.g. 22]
-->

### Additional Information

<!-- Anything else we should know? -->
