https://bugs.webkit.org/show_bug.cgi?id=91448

Reviewed by Adrienne Walker.

Unifies redundant traversal logic and static cast previously used
to determine if an element or document can be made fullscreen.
This clean up prepares for pointer lock, which will use the same logic.

Added a test to detect an edge case of an owning document with
fullscreen permision moving an iframe to fullscreen, while that iframe
does not have permision for its contents to be made fullscreen.

Source/WebCore:

Test: fullscreen/full-screen-iframe-without-allow-attribute-allowed-from-parent.html

* dom/Document.cpp:
(WebCore::isAttributeOnAllOwners):
(WebCore::Document::fullScreenIsAllowedForElement):
(WebCore::Document::webkitFullscreenEnabled):

LayoutTests:

* fullscreen/full-screen-iframe-without-allow-attribute-allowed-from-parent-expected.txt: Added.
* fullscreen/full-screen-iframe-without-allow-attribute-allowed-from-parent.html: Added.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@123005 268f45cc-cd09-0410-ab3c-d52691b4dbfc