Move createDom call into the constructor of block drag surface. (#790)

core/block_drag_surface.js

@@ -47,6 +47,7 @@ Blockly.BlockDragSurfaceSvg = function(container) {
    * @private
    */
   this.container_ = container;
+  this.createDom();
 };
 
 /**

core/inject.js

@@ -60,7 +60,6 @@ Blockly.inject = function(container, opt_options) {
   // Create surfaces for dragging things. These are optimizations
   // so that the broowser does not repaint during the drag.
   var blockDragSurface = new Blockly.BlockDragSurfaceSvg(subContainer);
-  blockDragSurface.createDom();
   var workspaceDragSurface = new Blockly.workspaceDragSurfaceSvg(subContainer);
 
   var workspace = Blockly.createMainWorkspace_(svg, options, blockDragSurface,