move onAdd of Layer to layer._initRenderer

Author: fuzhenn

src/layer/Layer.js

@@ -395,6 +395,9 @@ class Layer extends JSONAble(Eventable(Renderable(Class))) {
         this._renderer.layer = this;
         this._renderer.setZIndex(this.getZIndex());
         this._switchEvents('on', this._renderer);
+        if (this._renderer.onAdd) {
+            this._renderer.onAdd();
+        }
     }
 
     _doRemove() {

src/renderer/layer/CanvasRenderer.js

@@ -614,9 +614,6 @@ class CanvasRenderer extends Class {
             // not to create canvas when layer is empty
             return;
         }
-        if (!this._painted && this.onAdd) {
-            this.onAdd();
-        }
         this._drawAndRecord();
     }