Reuse flydown SVG rather than making orphans (#1876)

Change-Id: I34fc7bb333208d59e9186800fe2696621c9971af

appinventor/blocklyeditor/src/field_flydown.js

@@ -151,12 +151,11 @@ Blockly.FieldFlydown.prototype.showFlydown_ = function() {
   Blockly.hideChaff(); // Hide open context menus, dropDowns, flyouts, and other flydowns
   Blockly.FieldFlydown.openFieldFlydown_ = this; // Remember field to which flydown is attached
   var flydown = Blockly.getMainWorkspace().getFlydown();
-  var flydownSvg = flydown.createDom(this.flyoutCSSClassName);
   // Add flydown to top-level svg, *not* to main workspace svg
   // This is essential for correct positioning of flydown via translation
   // (If it's in workspace svg, it will be additionally translated by
   //  workspace svg translation relative to Blockly.svg.)
-  Blockly.getMainWorkspace().getParentSvg().appendChild(flydownSvg);
+  Blockly.getMainWorkspace().getParentSvg().appendChild(flydown.svgGroup_);
   // adjust scale for current zoom level
   flydown.workspace_.setScale(flydown.targetWorkspace_.scale);
   flydown.setCSSClass(this.flyoutCSSClassName); // This could have been changed by another field.