Deprecations and Removals in Chrome 64
In nearly every version of Chrome, we see a significant number of updates and improvements to the product, its performance, and also capabilities of the Web Platform. This article describes some of the deprecations and removals in Chrome 64, which is in beta as of December 14.
Remove support for multiple shadow roots
Shadow DOM version 0 allowed multiple shadow roots. At a standards meeting in April 2015 it was decided that this feature should not be part of version 1. Support was deprecated shortly thereafter in Chrome 45. In Chrome 64 support is now removed.
getMatchedCSSRules() method is a non-standard, WebKit-only API that retrieves a list of style rules applied to a particular element. This has been deprecated since 2014. It's now being removed because it's not on a standards track.
Since there is currently no standards-based alternative, developers would need to create their own. There is at least one example on StackOverflow.