Save PNG Canvas Image to HTML5 Storage (JAVASCRIPT)?

I am developing a chrome extension.

I open an image file in canvas, I apply some changes to it, then I am trying to save it to the HTML5 filesystem api.

First I get the dataURL from the canvas:

    var dataURL = canvas.toDataURL('image/png;base64'); 

Then just the data:

    var image64 = dataURL.replace(/data:image\/png;base64,/, '');

Then I make a Blob.

    var bb = new BlobBuilder();
    bb.append(image64);
    var blob = bb.getBlob('image/png');

Then I request the file system with the following function onInitFs();

    function onInitFs(fs) {
      fs.root.getFile('image.png', {create: true}, function(fileEntry) {
        // Create a FileWriter object for our FileEntry (log.txt).
        fileEntry.createWriter(function(fileWriter) {
        //WRITING THE BLOB TO FILE
        fileWriter.write(blob);
        }, errorHandler);
      }, errorHandler);
    }

    window.requestFileSystem(window.PERSISTENT, 5*1024*1024, onInitFs, errorHandler);

This results in a corrupted file being written to the file system.

I don't know what else I can do to make this work.

Could someone please guide me in the right direction.

The following are some of the sources to the functions I am using to accomplish this task.

http://dev.w3.org/html5/canvas-api/canvas-2d-api.html#todataurl-method

http://www.html5rocks.com/en/tutorials/file/filesystem/#toc-file-creatingempty

Thank You!