Enable causal stacktrace in kernel

runtime/vm/kernel_reader.cc

Index: runtime/vm/kernel_reader.cc
diff --git a/runtime/vm/kernel_reader.cc b/runtime/vm/kernel_reader.cc
index 752e42e667910e2f0b488177fb4fd96d654f8c8a..cf8f45a5b638f3f62e08fb303d4112a63b3761d0 100644
--- a/runtime/vm/kernel_reader.cc
+++ b/runtime/vm/kernel_reader.cc
@@ -427,7 +427,23 @@ void KernelReader::ReadProcedure(const dart::Library& library,
   function.set_end_token_pos(kernel_procedure->end_position());
   owner.AddFunction(function);
   function.set_kernel_function(kernel_procedure);
-  function.set_is_debuggable(kernel_procedure->function()->debuggable());
+  function.set_is_debuggable(
+      kernel_procedure->function()->original_async_marker() ==
+      FunctionNode::kSync);
+  switch (kernel_procedure->function()->original_async_marker()) {
+    case FunctionNode::kSyncStar:
+      function.set_modifier(RawFunction::kSyncGen);
+      break;
+    case FunctionNode::kAsync:
+      function.set_modifier(RawFunction::kAsync);
+      break;
+    case FunctionNode::kAsyncStar:
+      function.set_modifier(RawFunction::kAsyncGen);
+      break;
+    default:
+      // no special modifier
+      break;
+  }
   if (native_name != NULL) {
     function.set_native_name(*native_name);
   }