...when it isn't.
When CCleaner runs in the background, it skips Chrome. If I run CCleaner with the UI open, I get a popup saying Google Chrome needs to be closed. Even when it is closed. There are no Chrome related processes running. The 'Continue running background apps when Chrome is closed' setting is disabled and so is cloud print.
If I have CCleaner close Chrome in that same popup the CCleaner seems to become completely inactive. It doesn't freeze or hang, it just doesn't do anything while "closing application" is busy animating.