Pointer Lock handles disconnected DOM elements

https://bugs.webkit.org/show_bug.cgi?id=77029

Reviewed by Adrienne Walker.

Source/WebCore:

Pointer Lock Controller now checks when elements or documents are
removed, and unlocks if the target element is being removed.

Tests: pointer-lock/locked-element-iframe-removed-from-dom.html
       pointer-lock/locked-element-removed-from-dom.html

* dom/Document.cpp:
(WebCore::Document::detach):
* dom/Element.cpp:
(WebCore::Element::removedFrom):
(WebCore::Element::webkitRequestPointerLock):
* page/PointerLockController.cpp:
(WebCore::PointerLockController::requestPointerLock):
(WebCore::PointerLockController::elementRemoved):
(WebCore):
(WebCore::PointerLockController::documentDetached):
(WebCore::PointerLockController::didLosePointerLock):
(WebCore::PointerLockController::enqueueEvent):
* page/PointerLockController.h:
(WebCore):
(PointerLockController):

LayoutTests:

Two new tests that verify pointer lock is released when the target
is removed from the document.

* pointer-lock/locked-element-iframe-removed-from-dom-expected.txt: Added.
* pointer-lock/locked-element-iframe-removed-from-dom.html: Added.
* pointer-lock/locked-element-removed-from-dom-expected.txt: Added.
* pointer-lock/locked-element-removed-from-dom.html: Added.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@122626 268f45cc-cd09-0410-ab3c-d52691b4dbfc