Fix event warning crash when a listener is removed while dispatching event

components/test_runner/layout_test_runtime_flags.h

Index: components/test_runner/layout_test_runtime_flags.h
diff --git a/components/test_runner/layout_test_runtime_flags.h b/components/test_runner/layout_test_runtime_flags.h
index 1d5900402890b3e6a72b9f572b8e53df7d3063d2..e649e3b1315fa68df7628cb9a583f89cdf6ddd66 100644
--- a/components/test_runner/layout_test_runtime_flags.h
+++ b/components/test_runner/layout_test_runtime_flags.h
@@ -152,6 +152,10 @@ class TEST_RUNNER_EXPORT LayoutTestRuntimeFlags {
   // If true, the test_shell will print out the icon change notifications.
   DEFINE_BOOL_LAYOUT_TEST_RUNTIME_FLAG(dump_icon_changes)
 
+  // If true, the console messages produced by the page will
+  // be part of test output.
+  DEFINE_BOOL_LAYOUT_TEST_RUNTIME_FLAG(dump_console_messages)
+
   // Desired return value of WebFrameClient::runModalBeforeUnloadDialog.
   DEFINE_BOOL_LAYOUT_TEST_RUNTIME_FLAG(
       stay_on_page_after_handling_before_unload)