Add support for shadowRoot so it can also be observed.

[pitus]

The title says it all ...
I'm working on a page using lots of custom elements (Polymer/LitElement specifically) and would like to see what DOM changes they make, however DOMListener doesn't show any changes for me as all of the UI is within shadow DOM of custom components.
I have the same problem with MutationObserver - turns out, it needs to be attached to each shadowRoot separately :(
Perhaps you'll find a way to make it working with all of the DOM, including shadow DOM (as an user-selectable option)

[kdzwinel]

Thanks for reporting! It's definitely a good idea. If you have time to add it, please do. I'll be happy to code review and deploy to web store.