[iOS] MediaDocument should set a viewport
https://bugs.webkit.org/show_bug.cgi?id=134658
<rdar://problem/17552339>

Reviewed by Zalan Bujtas.

A MediaDocument should fill the viewport, so set its
initial-scale to 1 and make it non-zoomable.

* html/MediaDocument.cpp:
(WebCore::MediaDocumentParser::createDocumentStructure): Create
a <head> element and a <meta> element with a 1:1 viewport.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@170827 268f45cc-cd09-0410-ab3c-d52691b4dbfc