Created methods to surface zone memory information for each isolate and thread in JSON.

runtime/vm/zone.h

Index: runtime/vm/zone.h
diff --git a/runtime/vm/zone.h b/runtime/vm/zone.h
index 4e2e8a91e182a2f1cf8a012a687fc725ca816289..fabe8ae5c72f49713c2b7364589655e781688c63 100644
--- a/runtime/vm/zone.h
+++ b/runtime/vm/zone.h
@@ -8,6 +8,7 @@
 #include "platform/utils.h"
 #include "vm/allocation.h"
 #include "vm/handles.h"
+#include "vm/json_stream.h"
 #include "vm/thread.h"
 #include "vm/memory_region.h"
 
@@ -72,6 +73,10 @@ class Zone {
 
   Zone* previous() const { return previous_; }
 
+#ifndef RELEASE
+  void PrintToJSONObject(JSONObject* obj) const;
+#endif
+
  private:
   Zone();
   ~Zone();  // Delete all memory associated with the zone.