Fix a couple of bugs with async stack traces

runtime/vm/debugger.h

Index: runtime/vm/debugger.h
diff --git a/runtime/vm/debugger.h b/runtime/vm/debugger.h
index 3b9dbe35c9f75178701585efe4b998b3e1dfdda4..63de2f5a8eb04449823f520dd128a77409da83a6 100644
--- a/runtime/vm/debugger.h
+++ b/runtime/vm/debugger.h
@@ -605,6 +605,8 @@ class Debugger {
   // Callback to the debugger to continue frame rewind, post-deoptimization.
   void RewindPostDeopt();
 
+  static DebuggerStackTrace* CollectAwaiterReturnStackTrace();
+
  private:
   RawError* PauseRequest(ServiceEvent::EventKind kind);
 
@@ -679,7 +681,6 @@ class Debugger {
                                Array* deopt_frame);
   static DebuggerStackTrace* CollectStackTrace();
   static DebuggerStackTrace* CollectAsyncCausalStackTrace();
-  static DebuggerStackTrace* CollectAwaiterReturnStackTrace();
   void SignalPausedEvent(ActivationFrame* top_frame, Breakpoint* bpt);
 
   intptr_t nextId() { return next_id_++; }