What about Google building this into the Chrome app?
When you launch the app for the first time, it could ask "Do you want to open URLs in Chrome by default in Chrome-enabled apps?", and make it possible to change this in Chrome's settings menu.
This setting could then be stored in a UIPasteboard named something like com.google.chrome.default, and apps that want to implement the functionality suggested in the original post would just look in this pasteboard for the current setting.
According to Apple's documentation, "The UIPasteboard class enables an application to share data within the application or with another application using system-wide or application-specific pasteboards." http://developer.apple.com/library/ios/#DOCUMENTATION/UIKit/...
For a couple examples: OpenUDID and SecureUDID use UIPasteboard.
When you launch the app for the first time, it could ask "Do you want to open URLs in Chrome by default in Chrome-enabled apps?", and make it possible to change this in Chrome's settings menu.
This setting could then be stored in a UIPasteboard named something like com.google.chrome.default, and apps that want to implement the functionality suggested in the original post would just look in this pasteboard for the current setting.