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

runtime/vm/thread_registry.cc

Index: runtime/vm/thread_registry.cc
diff --git a/runtime/vm/thread_registry.cc b/runtime/vm/thread_registry.cc
index c660843c1eac3bd892de539293114b2dae1632c6..fc68f52d5549f2072c4ec6ce14fd3576b48af98b 100644
--- a/runtime/vm/thread_registry.cc
+++ b/runtime/vm/thread_registry.cc
@@ -5,6 +5,7 @@
 #include "vm/thread_registry.h"
 
 #include "vm/isolate.h"
+#include "vm/json_stream.h"
 #include "vm/lockers.h"
 
 namespace dart {
@@ -91,6 +92,24 @@ void ThreadRegistry::PrepareForGC() {
 }
 
 
+#ifndef PRODUCT
+void ThreadRegistry::PrintJSON(JSONStream* stream) const {
+  MonitorLocker ml(threads_lock());
+  JSONArray threads(stream);
+  PrintJSONHelper(&threads, active_list_);
+  PrintJSONHelper(&threads, free_list_);

[Cutch, 2016/12/08 22:25:54]

We shouldn't include the free list. These are Thread objects which aren't
actually owned anymore.

[bkonyi, 2016/12/08 22:42:01]

I'll go ahead and remove this then.

+}
+
+
+void ThreadRegistry::PrintJSONHelper(JSONArray* array, Thread* thread) const {
+  while (thread != NULL) {
+    array->AddValue(thread);
+    thread = thread->next_;
+  }
+}
+#endif
+
+
 void ThreadRegistry::AddToActiveListLocked(Thread* thread) {
   ASSERT(thread != NULL);
   ASSERT(threads_lock()->IsOwnedByCurrentThread());