- Type chrome://flags into the URL bar
- Search (Ctrl-F) for "Enable Rich Notifications"
- Make sure it's set to "Disabled"
- Search for (Ctrl-F) "Enable Experimental UI for Notifications"
- Make sure it's set to "Disabled"
- Search for (Ctrl-F) "Google Now"
- Make sure it's set to "Disabled"
- Click the "Relaunch Chrome" button at the bottom
- Rinse and repeat every time Google pushes a background update to your browser that turns it all back on
Also, you should probably do yourself a favour and uncheck the "Continue running background apps when Google Chrome is closed" box in the Settings menu.
Remember when we all switched to Chrome because it was the cleanest-running browser that used the least resources, and didn't have a history of running a bunch of crap in the background that we didn't need?
Those were the days...