That's a good question.
I'd say it's not possible at the moment, Ashley will be the one that can give more details about the chrome export side of things.
Edit: Oh yeah right Ninja'd, when does that British sleep ? ^^
On the other hand, why provide the html docs in download with the app ?
The iframe allow you to host/access it online. You could upload it on dropbox, and still access it from your application.
The only drawback I see is the downloading size. But the "On loaded" event of the iframe would allow you to make some timer/symbol that signals the user it's downloading.
Once you downloaded the doc, it stays in the user's cache. Only the first time/downloading of the manual would be an "issue".
And this would still work as intended in the chrome export I think.