How to debug web workers
Dev Channel version of Chrome supports debugging of workers by injecting fake workers implementation that simulates workers using an iframe within worker's client page. You will need to navigate to Scripts pane and tick Debug checkbox on Workers sidebar on the right, then reload the page. The worker script will then appear in the list of page scripts. This simulation has certain limitations, though -- since worker script will run in the client page thread, any long-running operations in worker will freeze the browser UI.
As a fast solution on the missing console.log, you can just use throw JSON.stringify({data:data})
The WebWorker can be debug just like a normal webpage. Chrome provides debugging dev-tools for WebWorkers at: chrome://inspect/#workers
Locate the desired running webworker and click "inspect". A separate dev-tool window will open dedicated to that webworker. The official instructions is worth checking.