<https://bugs.webkit.org/show_bug.cgi?id=90216>

<https://bugs.webkit.org/show_bug.cgi?id=90216>
<rdar://problem/11766518>
Undo handling in WebKit2 is not robust against some page-closing code paths

Reviewed by Enrica Casucci.

* UIProcess/API/mac/PageClientImpl.h:
Declared public function viewWillMoveToAnotherWindow().

* UIProcess/API/mac/PageClientImpl.mm:
(WebKit::PageClientImpl::viewWillMoveToAnotherWindow):
New function, calls clearAllEditCommands() to remove any Undo actions from the stack.
This guarantees that no Undo actions will be abandoned when the PageClientImpl is dealloc'ed.

* UIProcess/API/mac/WKView.mm:
(-[WKView viewWillMoveToWindow:]):
Now informs PageClientImpl via new function PageClientImpl::viewWillMoveToAnotherWindow().

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@121482 268f45cc-cd09-0410-ab3c-d52691b4dbfc