If you make a quick search, you’ll find how many people are annoyed by Chrome’s download bar, which doesn’t hide itself automatically, and requires you to manually hit the “X” button. There is no way to automate this through the extensions API, nor the browser gives you any option.
However, I found a simple trick to close the download bar, and it’s so simple that it’s hard to imagine how no one had this idea before – I didn’t see it anywhere, by the way. Not exactly automatic, but it’s better than click that “X” button.
Here’s how: you’ll have to use two shortcut keystrokes. The first one is Ctrl+J, which opens the download tab. The silver bullet is that this download tab displays the download progress, thus automatically closing the download bar. Then, once you have the download tab opened, just hit Ctrl+W, which closes the current tab, and it’s done.
So, by hitting Ctrl+J and Ctrl+W in succession, you’ll be free from clicking the “X” button on the download bar.