Debugger support for step-into async and async* functions.

runtime/vm/debugger.h

Index: runtime/vm/debugger.h
diff --git a/runtime/vm/debugger.h b/runtime/vm/debugger.h
index 0e1b2ed0ac06176bebf5d8da9176f16d01a0b61e..40a9063202c92b82a7827aa90e65b07b8ab9851a 100644
--- a/runtime/vm/debugger.h
+++ b/runtime/vm/debugger.h
@@ -454,6 +454,8 @@ class Debugger {
   void NotifyIsolateCreated();
   void Shutdown();
 
+  void OnIsolateRunnable();
+
   void NotifyCompilation(const Function& func);
   void NotifyDoneLoading();
 
@@ -484,12 +486,18 @@ class Debugger {
   void RemoveBreakpoint(intptr_t bp_id);
   Breakpoint* GetBreakpointById(intptr_t id);
 
+  void MaybeAsyncStepInto(const Closure& async_op);
+
+  void Continue();
+
   bool SetResumeAction(ResumeAction action,
                        intptr_t frame_index = 1,
                        const char** error = NULL);
 
   bool IsStepping() const { return resume_action_ != kContinue; }
 
+  bool IsSingleStepping() const { return resume_action_ == kStepInto; }
+
   bool IsPaused() const { return pause_event_ != NULL; }
 
   // Put the isolate into single stepping mode when Dart code next runs.