The iPhone has never had a built-in QR code scanner. That's probably because it's not every day (or every month) you scan a QR code spotted in the wild.
Despite the dwindling popularity of QR codes -- except for app-specific QR codes, like Snapchat's Snapcodes -- Chrome for iOS now makes it extra-easy to scan a QR code, should you ever spot one. The new feature also works for bar codes you find on product packaging.
How to scan QR codes (and bar codes) with Chrome
First, make sure you have the latest version of Chrome. Then, you can access the scanner in two ways:
1. 3D Touch the Chrome app icon and choose Scan QR Code.
2. Pull down to reveal the Spotlight search box, search for "QR" and select Scan QR Code from Chrome's listing.
If you scan a bar code, Chrome will launch a Google search for that product.