Rename HTMLSlotElement.getDistributedNodes to getAssignedNodes

Rename HTMLSlotElement.getDistributedNodes to getAssignedNodes
https://bugs.webkit.org/show_bug.cgi?id=153534

Reviewed by Antti Koivisto.

Source/WebCore:

Did the rename.

* html/HTMLSlotElement.idl:

LayoutTests:

Updated the tests to refect the rename. Also added test cases after r192763
to assert we don't assign comment and processing instruction nodes to a slot.

* fast/shadow-dom/HTMLSlotElement-interface-expected.txt:
* fast/shadow-dom/HTMLSlotElement-interface.html:
* fast/shadow-dom/NonDocumentTypeChildNode-interface-assignedSlot.html:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@195681 268f45cc-cd09-0410-ab3c-d52691b4dbfc