Moved zones and zone related stuff in its own directory.

src/handles.h

Index: src/handles.h
diff --git a/src/handles.h b/src/handles.h
index a7eb31efca959bca1374f4c98c6e81d5262eb155..fe6613f1fa8c137dd369e677379f5879bb03de85 100644
--- a/src/handles.h
+++ b/src/handles.h
@@ -10,7 +10,7 @@
 #include "src/base/macros.h"
 #include "src/checks.h"
 #include "src/globals.h"
-#include "src/zone.h"
+#include "src/zone/zone.h"
 
 namespace v8 {
 namespace internal {