Support shadows on the root RenderNode

bug:13211941

Cleans up some of the RenderNode method naming

Also removes unnecessary clip/save/restores, clipping shadows
predictably, as drawn by the parent, before drawing (and clipping,
etc.) the shadow casting child.

Change-Id: I795115e1fb869bbbdd7be43e279b97490fecc7e0
diff --git a/libs/hwui/Layer.cpp b/libs/hwui/Layer.cpp
index 4457c61..27409a2 100644
--- a/libs/hwui/Layer.cpp
+++ b/libs/hwui/Layer.cpp
@@ -209,7 +209,7 @@
             dirtyRect.right, dirtyRect.bottom, !isBlend());
 
     displayList->computeOrdering();
-    displayList->defer(deferredState, 0);
+    displayList->deferNodeTree(deferredState);
 
     deferredUpdateScheduled = false;
 }