Meta tags not populating with existing data

[MarkAtXert]

Steps to reproduce

1. Navigate to ​http://sdk.ckeditor.com/samples/fullpage.html and click source button.
2. Note existence of title and meta tags in source code
3. Click source button again to return to rendered view
4. Click document properties button
5. In general tab of document properties panel, note 'page title' field is populated with data from source
6. In document properties panel, click meta tags tab
7. Note meta tags field are not populated with data from source

Expected result

As a user I would expect the Meta Tags fields (Author, Copyright, etc.) to populate with existing data, much as the Page Title, Document Type Heading, etc. do.

Actual result

Meta Tags field do not populate with existing data from source

Other details (browser, OS, CKEditor version, installed plugins)

Chrome, Win 7, n/a

[Jakub Ś]

This is a DUP of #12624