Unreviewed EFL build fix since r170224.

Add retainPlatformLayer() and releasePlatformLayer() in ScrollingStateNodeCoordinatedGraphics.cpp
as well. Thouse functions were missed in r170224.

* page/scrolling/ScrollingStateNode.h:
* page/scrolling/coordinatedgraphics/ScrollingStateNodeCoordinatedGraphics.cpp:
(WebCore::LayerRepresentation::retainPlatformLayer):
(WebCore::LayerRepresentation::releasePlatformLayer):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@170229 268f45cc-cd09-0410-ab3c-d52691b4dbfc