Convert createDom calls to createUntypedDom (#481)

Unless they could be converted to use goog.dom.TagName, in which case do
that. createDom is going to require goog.dom.TagName member as the
tagName parameter. This change prepares for that.

core/tooltip.js

@@ -32,6 +32,7 @@
 goog.provide('Blockly.Tooltip');
 
 goog.require('goog.dom');
+goog.require('goog.dom.TagName');
 
 
 /**
@@ -120,7 +121,8 @@ Blockly.Tooltip.createDom = function() {
     return;  // Already created.
   }
   // Create an HTML container for popup overlays (e.g. editor widgets).
-  Blockly.Tooltip.DIV = goog.dom.createDom('div', 'blocklyTooltipDiv');
+  Blockly.Tooltip.DIV =
+      goog.dom.createDom(goog.dom.TagName.DIV, 'blocklyTooltipDiv');
   document.body.appendChild(Blockly.Tooltip.DIV);
 };