Change PopupMenuClient::listSize to return an int to appease warnings from MSVC /W3

Change PopupMenuClient::listSize to return an int to appease warnings from MSVC /W3

Reviewed by John.

No regression test possible.

* html/HTMLSelectElement.cpp:
(WebCore::HTMLSelectElement::menuListDefaultEventHandler):
* platform/PopupMenuClient.h:
* platform/win/PopupMenuWin.cpp:
(WebCore::PopupMenu::calculatePositionAndSize):
(WebCore::PopupMenu::focusFirst):
(WebCore::PopupMenu::focusLast):
(WebCore::PopupMenu::down):
(WebCore::PopupMenu::up):
(WebCore::PopupMenu::paint):
* rendering/RenderMenuList.cpp:
* rendering/RenderMenuList.h:
* rendering/RenderTextControl.cpp:
* rendering/RenderTextControl.h:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@23876 268f45cc-cd09-0410-ab3c-d52691b4dbfc