Sane asynchronous debugging and stack traces

runtime/vm/isolate.cc

Index: runtime/vm/isolate.cc
diff --git a/runtime/vm/isolate.cc b/runtime/vm/isolate.cc
index 5e43f3a05bc1d7d5a077b7801806c260bf0c81d8..566198f8a15c8689ee6a85caa61837100b5c76b3 100644
--- a/runtime/vm/isolate.cc
+++ b/runtime/vm/isolate.cc
@@ -1168,8 +1168,10 @@ bool Isolate::MakeRunnable() {
   ASSERT(object_store()->root_library() != Library::null());
   set_is_runnable(true);
 #ifndef PRODUCT
-  if (FLAG_support_debugger && !ServiceIsolate::IsServiceIsolate(this)) {
-    if (FLAG_pause_isolates_on_unhandled_exceptions) {
+  if (FLAG_support_debugger) {
+    debugger()->WhenRunnable();
+    if (FLAG_pause_isolates_on_unhandled_exceptions &&
+        !ServiceIsolate::IsServiceIsolate(this)) {
       debugger()->SetExceptionPauseInfo(kPauseOnUnhandledExceptions);
     }
   }