Hello. I have been using Linux Mint LXDE for a couple of days and I have noticed that after opening and closing some applications in system tray some blank spaces remain, something like this:
right click on panel to look at panel applets. Play with any spacers included, and some applets have a attribute called expand.
Don't use chromimum (spelling?) but I believe if you right click on it's 'Window button' it brings up list of tabs (the showing applet is the active one)