Keep the wrapper of FetchEvent alive while waiting for the preload response.

third_party/WebKit/Source/modules/serviceworkers/FetchEvent.h

Index: third_party/WebKit/Source/modules/serviceworkers/FetchEvent.h
diff --git a/third_party/WebKit/Source/modules/serviceworkers/FetchEvent.h b/third_party/WebKit/Source/modules/serviceworkers/FetchEvent.h
index 14fb995af0a9508798c9dd0cc8b31c07afe672ab..5e4b7f74965a196dfc554e6308ed8cf0be5855e3 100644
--- a/third_party/WebKit/Source/modules/serviceworkers/FetchEvent.h
+++ b/third_party/WebKit/Source/modules/serviceworkers/FetchEvent.h
@@ -9,12 +9,14 @@
 
 #include "bindings/core/v8/ScriptPromise.h"
 #include "bindings/core/v8/ScriptPromiseProperty.h"
+#include "core/dom/ContextLifecycleObserver.h"
 #include "modules/EventModules.h"
 #include "modules/ModulesExport.h"
 #include "modules/fetch/Request.h"
 #include "modules/serviceworkers/ExtendableEvent.h"
 #include "modules/serviceworkers/FetchEventInit.h"
 #include "modules/serviceworkers/WaitUntilObserver.h"
+#include "platform/bindings/ActiveScriptWrappable.h"
 #include "platform/heap/Handle.h"
 #include "platform/loader/fetch/ResourceResponse.h"
 
@@ -33,8 +35,12 @@ class WorkerGlobalScope;
 // A fetch event is dispatched by the client to a service worker's script
 // context. FetchRespondWithObserver can be used to notify the client about the
 // service worker's response.
-class MODULES_EXPORT FetchEvent final : public ExtendableEvent {
+class MODULES_EXPORT FetchEvent final
+    : public ExtendableEvent,
+      public ActiveScriptWrappable<FetchEvent>,
+      public ContextClient {
   DEFINE_WRAPPERTYPEINFO();
+  USING_GARBAGE_COLLECTED_MIXIN(FetchEvent);
 
  public:
   using PreloadResponseProperty = ScriptPromiseProperty<Member<FetchEvent>,
@@ -50,6 +56,8 @@ class MODULES_EXPORT FetchEvent final : public ExtendableEvent {
                             WaitUntilObserver*,
                             bool navigation_preload_sent);
 
+  ~FetchEvent() override;
+
   Request* request() const;
   String clientId() const;
   bool isReload() const;
@@ -70,6 +78,9 @@ class MODULES_EXPORT FetchEvent final : public ExtendableEvent {
 
   const AtomicString& InterfaceName() const override;
 
+  // ScriptWrappable
+  bool HasPendingActivity() const override;
+
   DECLARE_VIRTUAL_TRACE();
 
  protected: