This is exactly the issue. They are working on an experimental solution to let garbage collection happen for DOM nodes that are created from Dart or V8. This

This is exactly the issue. They are working on an experimental solution to let garbage collection happen for DOM nodes that are created from Dart or V8. This basically requires a rewrite of the memory management of DOM nodes. This is still very much a work in progress and not ready for prime time. The solution the team uses for Dartium is not the same as what they want to do for the shipping version of Chrome, so it'll be a bit before that's ready.