Fixes Issue: #<issue number>

Here's the Pull Request Doc
https://devtools-html.github.io/debugger.html/CONTRIBUTING.html#pull-requests

### Summary of Changes

* change 1
* change 2

### Test Plan

Tell us a little a bit about how you tested your patch.

Example test plan:

- [x] Command-P opens the panel
- [x] Clicking “+” opens the panel
- [x] Clicking a source navigates to the source
- [x] Clicking "x" closes the panel

Here's the Debugger's Testing doc
https://docs.google.com/document/d/1oBMRxV8A2ag2t22YsQOxTdEv0mXKzIg0tggJjRkU1S0/edit#.
Feel free to improve it!

### Screenshots/Videos (OPTIONAL)
