- Make sure to prepare all threads for GC.

runtime/vm/thread.h

Index: runtime/vm/thread.h
diff --git a/runtime/vm/thread.h b/runtime/vm/thread.h
index 39ae291177b3635a8444865a84c486a9203d79e1..281ac843bde9ea39878e557a18533c19ffd2bb0f 100644
--- a/runtime/vm/thread.h
+++ b/runtime/vm/thread.h
@@ -134,10 +134,8 @@ class Thread : public BaseThread {
                                    bool bypass_safepoint = false);
   static void ExitIsolateAsHelper(bool bypass_safepoint = false);
 
-  // Called when the current thread transitions from mutator to collector.
   // Empties the store buffer block into the isolate.
-  // TODO(koda): Always run GC in separate thread.
-  static void PrepareForGC();
+  void PrepareForGC();
 
   // OSThread corresponding to this thread.
   OSThread* os_thread() const { return os_thread_; }