Don't create debug context if debug listener is not set

src/runtime/runtime-debug.cc

Index: src/runtime/runtime-debug.cc
diff --git a/src/runtime/runtime-debug.cc b/src/runtime/runtime-debug.cc
index 591c8650e24b4305f0961a2e87924c377ab35534..9696b76264362664fcb10f98148684c082981aae 100644
--- a/src/runtime/runtime-debug.cc
+++ b/src/runtime/runtime-debug.cc
@@ -2833,7 +2833,11 @@ RUNTIME_FUNCTION(Runtime_ExecuteInDebugContext) {
 RUNTIME_FUNCTION(Runtime_GetDebugContext) {
   HandleScope scope(isolate);
   DCHECK(args.length() == 0);
-  Handle<Context> context = isolate->debug()->GetDebugContext();
+  Handle<Context> context;
+  {
+    DebugScope debug_scope(isolate->debug());
+    context = isolate->debug()->GetDebugContext();
+  }
   if (context.is_null()) return isolate->heap()->undefined_value();
   context->set_security_token(isolate->native_context()->security_token());
   return context->global_proxy();