[DevTools] Replace usages of document with custom functions.

Source/devtools/front_end/ui/DOMExtension.js

Index: Source/devtools/front_end/ui/DOMExtension.js
diff --git a/Source/devtools/front_end/ui/DOMExtension.js b/Source/devtools/front_end/ui/DOMExtension.js
index d862f94212839c823b06dc74b64cd0f377d55f74..9dd9b9daf441629bcf8c0af0f5d541817838fbf6 100644
--- a/Source/devtools/front_end/ui/DOMExtension.js
+++ b/Source/devtools/front_end/ui/DOMExtension.js
@@ -398,6 +398,24 @@ Element.prototype.isInsertionCaretInside = function()
 }
 
 /**
+ * @param {string} tagName
+ * @return {!Element}
+ */
+function createElement(tagName)
+{
+    return document.createElement(tagName);
+}
+
+/**
+ * @param {number|string} data
+ * @return {!Text}
+ */
+function createTextNode(data)
+{
+    return document.createTextNode(data);
+}
+
+/**
  * @param {string} elementName
  * @param {string=} className
  * @return {!Element}
@@ -415,6 +433,24 @@ Document.prototype.createElementWithClass = function(elementName, className)
  * @param {string=} className
  * @return {!Element}
  */
+function createElementWithClass(elementName, className)
+{
+    return document.createElementWithClass(elementName, className);
+}
+
+/**
+ * @return {!DocumentFragment}
+ */
+function createDocumentFragment()
+{
+    return document.createDocumentFragment();
+}
+
+/**
+ * @param {string} elementName
+ * @param {string=} className
+ * @return {!Element}
+ */
 Element.prototype.createChild = function(elementName, className)
 {
     var element = this.ownerDocument.createElementWithClass(elementName, className);