Hi,
If I understand you well, the previous developer completed something like 50% of the API, but nothing of the Chrome app code? Or he did develop the Chrome app, published it to Chrome Web Store, but didn't provide you with the source code?
Did you hire the developer via Freelancer.com? I just hate hearing stories like that, because it affects the confidence both the employers and freelancers have in the service, with the fake job postings and all...
Another thing, when you say a "plugin", are you refering to a Chrome extension or Chrome apps, because those two are kind of a two different animals and from what you are saying in the project description it seems to me that the Chrome extension would suffice here (it has more limited functionality than Chrome app, but on the other hand works in a more secure environment and users are more prone to install extensions than apps).
I've already done work with Chrome extensions here on Freelancer, nothing too complicated, but please feel free to take a look at my profile and reviews. From your project description I'd say this shouldn't be too complicated, either, but I'd like to know more details.
My experience with software development is extensive (more than 5+ years in web development) and I'm willing to send you my detailed CV/portfolio, but only upon initial contact, because I had some bad experience with sharing my CV upfront and have become more cautious since. Hope you understand.
Kind Regards,
Vladan Stojanovic