blink_gc_plugin: detect singletons with embedded ScriptWrappables.

tools/clang/blink_gc_plugin/BlinkGCPluginOptions.h

Index: tools/clang/blink_gc_plugin/BlinkGCPluginOptions.h
diff --git a/tools/clang/blink_gc_plugin/BlinkGCPluginOptions.h b/tools/clang/blink_gc_plugin/BlinkGCPluginOptions.h
index 0df51cd597cc73c3f310ba54e6fb174a3f8a2a29..84554f0ca464cc48734dae670c4b642fc76f53ff 100644
--- a/tools/clang/blink_gc_plugin/BlinkGCPluginOptions.h
+++ b/tools/clang/blink_gc_plugin/BlinkGCPluginOptions.h
@@ -22,6 +22,10 @@ struct BlinkGCPluginOptions {
   // TODO(https://crbug.com/675879): Clean up after the Blink rename.
   bool use_chromium_style_naming = false;
 
+  // If |true|, verify that static singletons do not refer to
+  // ScriptWrappables.
+  bool warn_singleton_with_scriptwrappables = false;
+
   std::set<std::string> ignored_classes;
   std::set<std::string> checked_namespaces;
   std::vector<std::string> ignored_directories;