Implement selectedOptions attribute of HTMLSelectElement.

Implement selectedOptions attribute of HTMLSelectElement.
https://bugs.webkit.org/show_bug.cgi?id=80631

Reviewed by Ryosuke Niwa.

Source/WebCore:

Add a new collection as a member of HTMLSelectElement which is
used to store the selected elements. Extend HTMLCollection to
support the new collection type needed by this feature. Make sure
that we invalidate the collection when the select state of an
option changes as the select state change does not trigger a dom
tree version change.

Reference : http://www.whatwg.org/specs/web-apps/current-work/multipage/the-button-element.html#dom-select-selectedoptions

Test: fast/dom/HTMLSelectElement/select-selectedOptions.html

* html/CollectionType.h:
* html/HTMLCollection.cpp:
(WebCore::shouldIncludeChildren):
(WebCore::HTMLCollection::clearCache):
(WebCore):
(WebCore::HTMLCollection::isAcceptableElement):
* html/HTMLCollection.h:
(HTMLCollection):
* html/HTMLOptionElement.cpp:
(WebCore::HTMLOptionElement::setSelectedState):
* html/HTMLSelectElement.cpp:
(WebCore::HTMLSelectElement::selectedOptions):
(WebCore):
(WebCore::HTMLSelectElement::invalidateSelectedItems):
(WebCore::HTMLSelectElement::setRecalcListItems):
* html/HTMLSelectElement.h:
(WebCore):
(HTMLSelectElement):
* html/HTMLSelectElement.idl:

LayoutTests:

New tests to cover the feature.

* fast/dom/HTMLSelectElement/select-selectedOptions-expected.txt: Added.
* fast/dom/HTMLSelectElement/select-selectedOptions.html: Added.
* fast/dom/htmlcollection-non-html-expected.txt:
* fast/dom/htmlcollection-non-html.html:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@121392 268f45cc-cd09-0410-ab3c-d52691b4dbfc