Build 'window.location.origin' for Internet Explorer

As TinyMCE's CodeMirror plug-in uses 'window.location.origin' which is not supported by Internet Explorer, the HTML or raw code editor does not work under Internet Explorer.
We need to create one in order to make these vendor codes work under Internet Explorer.
Merge pull request #3893 from louyihua/tinymce-ie-fix

Make TinyMCE's HTML source code editor work under Internet Explorer