Fix alignment of blocks tab in Code demo.

demos/code/code.js

@@ -357,9 +357,9 @@ Code.init = function() {
       el.style.width = (2 * bBox.width - el.offsetWidth) + 'px';
     }
     // Make the 'Blocks' tab line up with the toolbox.
-    if (Blockly.Toolbox.width) {
+    if (Blockly.mainWorkspace.toolbox_.width) {
       document.getElementById('tab_blocks').style.minWidth =
-          (Blockly.Toolbox.width - 38) + 'px';
+          (Blockly.mainWorkspace.toolbox_.width - 38) + 'px';
           // Account for the 19 pixel margin and on each side.
     }
   };