- Make sure to prepare all threads for GC.

runtime/vm/gc_marker.cc

Index: runtime/vm/gc_marker.cc
diff --git a/runtime/vm/gc_marker.cc b/runtime/vm/gc_marker.cc
index 45e84d25fad6cbfde8a4ce603f56865a5cdd0607..6b2a946e98fb429f7f5951a01ad636e5aa37c80e 100644
--- a/runtime/vm/gc_marker.cc
+++ b/runtime/vm/gc_marker.cc
@@ -18,6 +18,7 @@
 #include "vm/store_buffer.h"
 #include "vm/thread_barrier.h"
 #include "vm/thread_pool.h"
+#include "vm/thread_registry.h"
 #include "vm/visitor.h"
 #include "vm/object_id_ring.h"
 
@@ -484,7 +485,7 @@ void GCMarker::Prologue(Isolate* isolate, bool invoke_api_callbacks) {
   if (invoke_api_callbacks && (isolate->gc_prologue_callback() != NULL)) {
     (isolate->gc_prologue_callback())();
   }
-  Thread::PrepareForGC();
+  isolate->thread_registry()->PrepareForGC();
   // The store buffers will be rebuilt as part of marking, reset them now.
   isolate->store_buffer()->Reset();
 }