message: Fix zrender won't when given dom is canvas.
diff: @@ -179,6 +179,7 @@ var Painter = function (root, storage, opts) {
  // Create layer if only one given canvas
  // Device pixel ratio is fixed to 1 because given canvas has its specified width and height
  var mainLayer = new Layer(root, this, 1);
  + mainLayer.__builtin__ = true;
  mainLayer.initContext();
  // FIXME Use canvas width and height
  // mainLayer.resize(width, height);
  