Support placement new syntax for zone objects and start using it in the parser.

src/zone.h

Index: src/zone.h
diff --git a/src/zone.h b/src/zone.h
index 13b55c4c7f3a11d1223f2cd7c0c900392f137147..9efe4f5d0511a533cb37ff9dc09355be23202d46 100644
--- a/src/zone.h
+++ b/src/zone.h
@@ -133,6 +133,7 @@ class ZoneObject {
  public:
   // Allocate a new ZoneObject of 'size' bytes in the Zone.
   inline void* operator new(size_t size);
+  inline void* operator new(size_t size, Zone* zone);
 
   // Ideally, the delete operator should be private instead of
   // public, but unfortunately the compiler sometimes synthesizes