Remove the lifetime hack in ImageLoader where it keeps its assoc element alive

third_party/WebKit/Source/core/html/HTMLPlugInElement.h

Index: third_party/WebKit/Source/core/html/HTMLPlugInElement.h
diff --git a/third_party/WebKit/Source/core/html/HTMLPlugInElement.h b/third_party/WebKit/Source/core/html/HTMLPlugInElement.h
index 7e4476377adff21541a491af3953cefe7b108a08..56fe72273b4cc006b94ad9d1fcaad77b5063d270 100644
--- a/third_party/WebKit/Source/core/html/HTMLPlugInElement.h
+++ b/third_party/WebKit/Source/core/html/HTMLPlugInElement.h
@@ -26,6 +26,7 @@
 
 #include "core/CoreExport.h"
 #include "core/html/HTMLFrameOwnerElement.h"
+#include "platform/bindings/ActiveScriptWrappable.h"
 #include "platform/bindings/SharedPersistent.h"
 #include "v8/include/v8.h"
 
@@ -41,11 +42,17 @@ enum PreferPlugInsForImagesOption {
   kShouldNotPreferPlugInsForImages
 };
 
-class CORE_EXPORT HTMLPlugInElement : public HTMLFrameOwnerElement {
+class CORE_EXPORT HTMLPlugInElement
+    : public HTMLFrameOwnerElement,
+      public ActiveScriptWrappable<HTMLPlugInElement> {
+  USING_GARBAGE_COLLECTED_MIXIN(HTMLPlugInElement);
+
  public:
   ~HTMLPlugInElement() override;
   DECLARE_VIRTUAL_TRACE();
 
+  bool HasPendingActivity() const final;
+
   void SetFocused(bool, WebFocusType) override;
   void ResetInstance();
   // TODO(dcheng): Consider removing this, since HTMLEmbedElementLegacyCall