Simplify memory model between managed and unmanaged memory

Summary: Instead of having different lifetimes for java and c memory we can can tie them together and make them much easier to manage. This also leads to automatically pooling native memory if pooling java memory.

Differential Revision: D4051454

fbshipit-source-id: 8f5d010be520b3d1c981a7f85e5e6d95773ea6c1

CSSLayout/CSSLayout.c

@@ -169,6 +169,15 @@ void CSSNodeFreeRecursive(const CSSNodeRef root) {
   CSSNodeFree(root);
 }
 
+void CSSNodeReset(const CSSNodeRef node) {
+  CSS_ASSERT(CSSNodeChildCount(node) == 0, "Cannot reset a node which still has children attached");
+  CSS_ASSERT(node->parent == NULL, "Cannot reset a node still attached to a parent");
+  
+  CSSNodeListFree(node->children);
+  memset(node, 0, sizeof(CSSNode));
+  CSSNodeInit(node);
+}
+
 int32_t CSSNodeGetInstanceCount(void) {
   return gNodeInstanceCount;
 }