Related commit: 
electron/electron@3ac4c1f

More info here: https://developers.google.com/web/updates/2018/03/cssom

This change uses a different JavaScript syntax to cause the "when a .js file
does not start with 'use babel'" spec to fail again after upgrading to Electron
3 / Node 10.3.0.  The previous generator syntax seems to be supported in the
version of V8 used by Node 10 so we now need to use the 'export default' syntax
to trigger an error.

I've verified that changing the first line of this file to 'use babel' causes
the file to load successfully, so it seems this new syntax is effective to
verify the desired behavior.

In Chrome 66+ it seems that getComputedStyle().fontWeight returns the computed
numeric value of the style instead of the original descriptive name.  We now
look for value '700' which corresponds to the value of 'bold'.

This change is necessary for Electron 3 to a bug in Node.js 10.2.x which causes
the `removeAllListeners` method to no longer remove all listeners for any event
name when no argument is passed:

nodejs/node#20924

This issue has been fixed in Node.js 10.3.0+ so we will have to remove this
workaround when we move to Electron 4.0 to avoid future event handler leaks.

As of Chromium 63, ::shadow CSS selectors have been fully removed:

https://developers.google.com/web/updates/2017/10/remove-shadow-piercing

As a result, any usage of ::shadow in a stylesheet seems to get removed as soon
as the stylesheet is applied to an HTMLStyleElement.  Since we have a couple of tests
that expect ::shadow selectors to be present, we must remove those expectations
since those selectors do not appear any longer.

This dependency is no longer needed now that we use Node's built-in APIs