The Java Class AutofillPaymentApp:

https://cs.chromium.org/chromium/src/chrome/android/java/src/org/chromium/chrome/browser/payments/AutofillPaymentApp.java?dr

has a lot of code that maps to components code. e.g., all the code looking up Network names exists in two places:

https://cs.chromium.org/chromium/src/components/payments/content/payment_request_converter.cc?type=cs&q=convert+network+file:%5Esrc/components/payments/+package:%5Echromium$&l=38