[DevTools] Replace usages of document with custom functions.

Source/devtools/front_end/source_frame/CodeMirrorUtils.js

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 166 matching lines @@
 
 /**
  * @return {!Element}
  */
 WebInspector.CodeMirrorUtils.createThemeStyle = function()
 {
     var backgroundColor = InspectorFrontendHost.getSelectionBackgroundColor();
     var backgroundColorRule = backgroundColor ? ".CodeMirror .CodeMirror-selected { background-color: " + backgroundColor + ";}" : "";
     var foregroundColor = InspectorFrontendHost.getSelectionForegroundColor();
     var foregroundColorRule = foregroundColor ? ".CodeMirror .CodeMirror-selectedtext:not(.CodeMirror-persist-highlight) { color: " + foregroundColor + "!important;}" : "";
-    var style = document.createElement("style");
+    var style = createElement("style");
     if (foregroundColorRule || backgroundColorRule)
         style.textContent = backgroundColorRule + foregroundColorRule;
     return style;
 }