Disable async debugger support until context mismatch issue is resolved.

runtime/vm/object_store.cc

Index: runtime/vm/object_store.cc
diff --git a/runtime/vm/object_store.cc b/runtime/vm/object_store.cc
index af5c25960f34ae34f9906dd927fda727d44849e6..bae0df343ae23e3d29800b6732fa2c14c230a9ba 100644
--- a/runtime/vm/object_store.cc
+++ b/runtime/vm/object_store.cc
@@ -273,7 +273,7 @@ void ObjectStore::InitKnownObjects() {
                                       function_name, 2, Object::null_array());
   ASSERT(!function.IsNull());
   set_complete_on_async_return(function);
-  if (FLAG_async_debugger_stepping) {
+  if (FLAG_async_debugger) {
     // Disable debugging and inlining the _CompleteOnAsyncReturn function.
     function.set_is_debuggable(false);
     function.set_is_inlinable(false);
@@ -284,7 +284,7 @@ void ObjectStore::InitKnownObjects() {
   ASSERT(!cls.IsNull());
   set_async_star_stream_controller(cls);
 
-  if (FLAG_async_debugger_stepping) {
+  if (FLAG_async_debugger) {
     // Disable debugging and inlining of all functions on the
     // _AsyncStarStreamController class.
     const Array& functions = Array::Handle(cls.functions());