From iMore's Google offers iOS developers a way to treat Chrome almost like the default browser by Richard Devine.
Google has released code that gives developers the ability to have links open directly in Google Chrome instead of Apple's built-in Safari browser, and return users right back to their app with a single tap. A developer has to add Google's code -- a URL scheme with x-callback -- to their app, and you have to have Chrome installed on your device, but the execution is seamless.
What is interesting about this is that it should not be the developer's to call to decide which app will handle links or e-mail for an user.
The ability to set default apps is a long time feature request by "power users" of the platform. It is also clear that the lack of this possibility undermines the experience of those who use Chrome as their default browser on iOS. However the closed and inflexible solution which is the current system wide behavior is far better and more reliable than the almost anarchic alternative in which each of the apps in an user's phone might treat another app as the default target of a given action, unbeknownst to the user himself.
On launching The Magazine, Marco Arment had implemented similar functionality by assuming that whenever someone had Chrome installed, what they wanted was to use it to browse the web in all situations. While a fair assumption, it proved itself wrong very quickly. Marco then added what should be the actual behavior app developers should adopt: In the absence of system wide default overriding, allow the user to choose in the application's settings which is the app that should handle each action. This is a far less agressive solution, as it allows users to decide if and when they actually want to use anything different than Apple's defaults on a per app basis, rather than having the developers of their apps make the decision on their behalf.