Open the Gallery app and tap the hamburger menu, then tap Settings. Scroll down and tap on About Gallery. Repeatedly tap the version number (which might be "14.0.00.23") ten times until you see a bubble that reads "[Labs] Gallery labs is enabled". Go back, scroll down again if necessary, and tap on Gallery Labs. The second slider option should be Album entry-locks - tap on the slider, read the pop-up, tap OK, and restart the Gallery app to enable it.
