<rdar://problem/4832894> Crash deleting an element inside a list while deletion rectangle is visible (compareBoundaryPoints)

        * Disable and hide the deletion UI for each editing command. This prevents editing commands from being affected
          by the deletion UI elements we insert. The deletion UI is then shown after the editing commands are completely done.

        * Multiple calls to DeleteButtonController's disable() needed to be paired with the same number of enable() calls before
          the deletion UI is enabled again. This allows for nested editing commands to be called without thrashing the deletion UI.

        * Make sure the the renderers are currently reflecting the latest style changes, so call updateLayoutIgnorePendingStylesheets().

        * editing/DeleteButtonController.cpp:
        (WebCore::DeleteButtonController::DeleteButtonController):
        (WebCore::isDeletableElement):
        (WebCore::DeleteButtonController::respondToChangedSelection): check the enabled state
        (WebCore::DeleteButtonController::respondToChangedContents): check the enabled state
        (WebCore::DeleteButtonController::show): call isDeletableElement() to make sure the element is allowed
        (WebCore::DeleteButtonController::deleteTarget): check the enabled state
        * editing/DeleteButtonController.h:
        (WebCore::DeleteButtonController::disable):
        (WebCore::DeleteButtonController::enable):
        (WebCore::DeleteButtonController::enabled):
        * editing/EditCommand.cpp:
        (WebCore::EditCommand::apply): hide and disable the deletion UI, then show at the end
        (WebCore::EditCommand::unapply): ditto
        (WebCore::EditCommand::reapply): ditto



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@17799 268f45cc-cd09-0410-ab3c-d52691b4dbfc