I bumbed into the same issue with Chrome ver39 on Lollipop but the solution below worked well.
Android onChange event not triggered in contentObserver for chrome history on android 5 (Lollypop)
However once I updated Chrome ver39.x to ver40, I found that the issue came up again that contentObservers did not get triggered anymore on android lolipop again even if the method above was called.
Has someone found this issue and any solution?