[chromium] Remove optionalness of second parameter to WebLayerTreeView::setViewportSize
https://bugs.webkit.org/show_bug.cgi?id=108972

Reviewed by Adam Barth.

This was added to ease the transition of adding this parameter, but it's now always set.

* chromium/public/WebLayerTreeView.h:
(WebLayerTreeView):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@141920 268f45cc-cd09-0410-ab3c-d52691b4dbfc