blink_gc_plugin: detect singletons with embedded ScriptWrappables.

tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp

Index: tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp
diff --git a/tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp b/tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp
index 099b2bd96bdd4f2ad0fbaa71b28bd2fd26ea046f..9380442453d559590ff73a25a88707ff4d1be0ac 100644
--- a/tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp
+++ b/tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp
@@ -37,6 +37,8 @@ class BlinkGCPluginAction : public PluginASTAction {
         options_.warn_stack_allocated_trace_method = true;
       } else if (arg == "warn-unneeded-finalizer") {
         options_.warn_unneeded_finalizer = true;
+      } else if (arg == "warn-unsafe-static-singletons") {
+        options_.warn_singleton_with_scriptwrappables = true;
       } else if (arg == "use-chromium-style-naming") {
         options_.use_chromium_style_naming = true;
       } else {