Steps to reproduce the problem:
1. Open a bunch of Facebook notifications.
2. Notice that tabs eventually become slow and CPU usage is very high

What went wrong?
In chrome://tracing, see lots of "startScrollbarPaintTimer" tasks

Chrome version: 54.0.2840.98  Channel: stable
OS Version: OS X 10.11.6
Flash Version: Shockwave Flash 23.0 r0