blink_gc_plugin should require tracing for classes that have a trace method

third_party/WebKit/Source/core/events/EventTarget.h

Index: third_party/WebKit/Source/core/events/EventTarget.h
diff --git a/third_party/WebKit/Source/core/events/EventTarget.h b/third_party/WebKit/Source/core/events/EventTarget.h
index 1e2272902f96e60557278406e5f512c378ee0244..9bec1dc11f3b4d9e51c04af08aff25e476ab9d39 100644
--- a/third_party/WebKit/Source/core/events/EventTarget.h
+++ b/third_party/WebKit/Source/core/events/EventTarget.h
@@ -219,8 +219,7 @@ class CORE_EXPORT EventTarget : public GarbageCollectedFinalized<EventTarget>,
 // object. However, we intentionally use it as a part of object for performance,
 // assuming that no one extracts a pointer of
 // EventTargetWithInlineData::m_eventTargetData and store it to a Member etc.
-class GC_PLUGIN_IGNORE("513199") CORE_EXPORT EventTargetWithInlineData
-    : public EventTarget {
+class CORE_EXPORT EventTargetWithInlineData : public EventTarget {
  public:
   ~EventTargetWithInlineData() override {}
 
@@ -234,6 +233,7 @@ class GC_PLUGIN_IGNORE("513199") CORE_EXPORT EventTargetWithInlineData
   EventTargetData& ensureEventTargetData() final { return m_eventTargetData; }
 
  private:
+  GC_PLUGIN_IGNORE("513199")
   EventTargetData m_eventTargetData;
 };