[DevTools] Replace usages of document with custom functions.

Source/devtools/front_end/source_frame/FontView.js

Index: Source/devtools/front_end/source_frame/FontView.js
diff --git a/Source/devtools/front_end/source_frame/FontView.js b/Source/devtools/front_end/source_frame/FontView.js
index 0de75d3fafcccc55c18b4077a1db50930b1ec714..5b4984989d7da31dd007b12f1198444d41b41733 100644
--- a/Source/devtools/front_end/source_frame/FontView.js
+++ b/Source/devtools/front_end/source_frame/FontView.js
@@ -53,11 +53,11 @@ WebInspector.FontView.prototype = {
 
         var uniqueFontName = "WebInspectorFontPreview" + (++WebInspector.FontView._fontId);
 
-        this.fontStyleElement = document.createElement("style");
+        this.fontStyleElement = createElement("style");
         this.fontStyleElement.textContent = "@font-face { font-family: \"" + uniqueFontName + "\"; src: url(" + this._url + "); }";
         document.head.appendChild(this.fontStyleElement);
 
-        var fontPreview = document.createElement("div");
+        var fontPreview = createElement("div");
         for (var i = 0; i < WebInspector.FontView._fontPreviewLines.length; ++i) {
             if (i > 0)
                 fontPreview.createChild("br");