Form control may be associated with the wrong HTML Form element after form id change

Form control may be associated with the wrong HTML Form element after form id change
https://bugs.webkit.org/show_bug.cgi?id=133456
<rdar://problem/17095055>

Reviewed by Andy Estes.

Source/WebCore:

Fixes an issue where a form control may be associated with the wrong HTML Form element
after the id of the HTML Form element associated with the form control is changed when
there is more than one HTML Form element with the same id in the document. Specifically,
a form control that has an HTML form attribute value X will always be associated with
some HTML Form element f where f.id = X regardless of whether f.id is subsequently
changed.

Tests: fast/forms/change-form-id-to-be-unique-then-submit-form.html
       fast/forms/change-form-id-to-be-unique.html

* dom/Element.cpp:
(WebCore::Element::attributeChanged): Notify observers when the id of an element changed.
(WebCore::Element::updateId): Added parameter NotifyObservers (defaults to NotifyObservers::Yes),
as to whether we should notify observers of the id change.
(WebCore::Element::updateIdForTreeScope): Ditto.
(WebCore::Element::willModifyAttribute): Do not notify observers of the id change immediately. As
indicated by the name of this method, we plan to modify the DOM attribute id of the element, but
we have not actually modified it when this method is called. Instead we will notify observers
in Element::attributeChanged(), which is called after the DOM attribute id is modified.
(WebCore::Element::cloneAttributesFromElement): Ditto.
* dom/Element.h: Defined enum class NotifyObservers.
* dom/TreeScope.cpp:
(WebCore::TreeScope::addElementById): Added boolean parameter notifyObservers (defaults to true)
as to whether we should dispatch a notification to all observers.
(WebCore::TreeScope::removeElementById): Ditto.
* dom/TreeScope.h:

LayoutTests:

Add tests to ensure that we associate the correct HTML Form element with a
<select> after changing the id of its associated HTML form element.

* fast/forms/change-form-id-to-be-unique-expected.txt: Added.
* fast/forms/change-form-id-to-be-unique-then-submit-form-expected.txt: Added.
* fast/forms/change-form-id-to-be-unique-then-submit-form.html: Added.
* fast/forms/change-form-id-to-be-unique.html: Added.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@183436 268f45cc-cd09-0410-ab3c-d52691b4dbfc