[chromium] Remove WebWidget::layerTreeView(), ownership is the other way around
https://bugs.webkit.org/show_bug.cgi?id=106139

Reviewed by Adrienne Walker.

This was added with the thought that it would be useful for transitioning code for a world where the
WebLayerTreeView for a given widget was owned by the WebWidgetClient instead of the WebWidget, but as it turns
out we've transitioned without every adding any callers to this.

* public/WebWidget.h:
(WebWidget):
* src/WebViewImpl.cpp:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@138859 268f45cc-cd09-0410-ab3c-d52691b4dbfc