Support type and encoderOptions parameters in toBlob polyfill.

src/General/lib/polyfill.coffee

@@ -3,12 +3,13 @@ Polyfill =
     @toBlob()
   toBlob: ->
     return if HTMLCanvasElement::toBlob
-    HTMLCanvasElement::toBlob = (cb) ->
-      data = atob @toDataURL()[22..]
+    HTMLCanvasElement::toBlob = (cb, type='image/png', encoderOptions) ->
+      url = @toDataURL type, encoderOptions
+      data = atob url[url.indexOf(',')+1..]
       # DataUrl to Binary code from Aeosynth's 4chan X repo
       l = data.length
       ui8a = new Uint8Array l
       for i in [0...l] by 1
         ui8a[i] = data.charCodeAt i
-      cb new Blob [ui8a], type: 'image/png'
+      cb new Blob [ui8a], {type}
     $.globalEval "HTMLCanvasElement.prototype.toBlob = (#{HTMLCanvasElement::toBlob});"