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

runtime/vm/thread_registry.h

Index: runtime/vm/thread_registry.h
diff --git a/runtime/vm/thread_registry.h b/runtime/vm/thread_registry.h
index eb2d327f64ebac1a7ce8828ea3eb341fcba6baaa..881a4d0b03b517f98b8c8c07ecf2f32f40efad25 100644
--- a/runtime/vm/thread_registry.h
+++ b/runtime/vm/thread_registry.h
@@ -14,6 +14,11 @@
 
 namespace dart {
 
+#ifndef PRODUCT
+class JSONStream;
+class JSONArray;
+#endif
+
 // Unordered collection of threads relating to a particular isolate.
 class ThreadRegistry {
  public:
@@ -28,6 +33,10 @@ class ThreadRegistry {
   void PrepareForGC();
   Thread* mutator_thread() const { return mutator_thread_; }
 
+#ifndef PRODUCT
+  void PrintJSON(JSONStream* stream) const;
+#endif
+
  private:
   Thread* active_list() const { return active_list_; }
   Monitor* threads_lock() const { return threads_lock_; }