Is this a bug report?

Yes.

Have you read the Contributing Guidelines?

Yes.

Environment

Environment:
OS: macOS High Sierra 10.13.2
Node: 9.4.0
Yarn: Not Found
npm: 5.6.0
Watchman: 4.9.0
Xcode: Xcode 9.2 Build version 9C40b
Android Studio: 3.0 AI-171.4443003

Packages: (wanted => installed)
react: ^16.2.0 => 16.2.0
react-native: ^0.52.0 => 0.52.0

Target Platform: iOS 8

Steps to Reproduce

Note: I upgraded to 0.52 last night using react-native-git-upgrade, it had been working previously on 0.51.

1. Run development app on real iOS device, which loads the JS bundle from http://192.168.0.13.xip.io:8081/index.delta?platform=ios&dev=true&minify=false
2. Enable JS Remote debug tools, which opens http://localhost:8081/debugger-ui/ in Chrome.
3. Bundle reloads and Chrome DevTools console displays the following error:

Failed to load http://192.168.0.13.xip.io:8081/index.delta?platform=ios&dev=true&minify=false: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost:8081' is therefore not allowed access. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.

Expected Behavior

App should load correctly and not throw an error when trying to debug JS remotely.

Actual Behavior

Failed to load http://192.168.0.13.xip.io:8081/index.delta?platform=ios&dev=true&minify=false: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost:8081' is therefore not allowed access. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.

Reproducible Demo

(Paste the link to an example project and exact instructions to reproduce the issue.)

Fresh react-native app using react-native init.

https://github.com/njbmartin/react-native-xip