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

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

Index: third_party/WebKit/Source/modules/serviceworkers/FetchEvent.cpp
diff --git a/third_party/WebKit/Source/modules/serviceworkers/FetchEvent.cpp b/third_party/WebKit/Source/modules/serviceworkers/FetchEvent.cpp
index a464f19d1283bdba45958c5665c665ec52c8d3cb..874c93562d661fae28bf730777d0a59fc9aabcf9 100644
--- a/third_party/WebKit/Source/modules/serviceworkers/FetchEvent.cpp
+++ b/third_party/WebKit/Source/modules/serviceworkers/FetchEvent.cpp
@@ -69,6 +69,13 @@ const AtomicString& FetchEvent::InterfaceName() const {
   return EventNames::FetchEvent;
 }
 
+bool FetchEvent::HasPendingActivity() const {
+  // Prevent V8 from garbage collecting the wrapper object while waiting for the
+  // preload response. This is in order to keep the resolver of preloadResponse
+  // Promise alive.
+  return waiting_for_preload_response_ && GetExecutionContext();
+}
+
 FetchEvent::FetchEvent(ScriptState* script_state,
                        const AtomicString& type,
                        const FetchEventInit& initializer,
@@ -76,11 +83,13 @@ FetchEvent::FetchEvent(ScriptState* script_state,
                        WaitUntilObserver* wait_until_observer,
                        bool navigation_preload_sent)
     : ExtendableEvent(type, initializer, wait_until_observer),
+      ContextClient(ExecutionContext::From(script_state)),
       observer_(respond_with_observer),
       preload_response_property_(new PreloadResponseProperty(
           ExecutionContext::From(script_state),
           this,
-          PreloadResponseProperty::kPreloadResponse)) {
+          PreloadResponseProperty::kPreloadResponse)),
+      waiting_for_preload_response_(navigation_preload_sent) {
   if (!navigation_preload_sent)
     preload_response_property_->ResolveWithUndefined();
 
@@ -109,6 +118,8 @@ FetchEvent::FetchEvent(ScriptState* script_state,
   }
 }
 
+FetchEvent::~FetchEvent() {}
+
 void FetchEvent::OnNavigationPreloadResponse(
     ScriptState* script_state,
     std::unique_ptr<WebURLResponse> response,
@@ -149,6 +160,7 @@ void FetchEvent::OnNavigationPreloadResponse(
 void FetchEvent::OnNavigationPreloadError(
     ScriptState* script_state,
     std::unique_ptr<WebServiceWorkerError> error) {
+  waiting_for_preload_response_ = false;
   if (!script_state->ContextIsValid())
     return;
   DCHECK(preload_response_property_);
@@ -163,6 +175,7 @@ void FetchEvent::OnNavigationPreloadComplete(
     int64_t encoded_body_length,
     int64_t decoded_body_length) {
   DCHECK(preload_response_);
+  waiting_for_preload_response_ = false;
   std::unique_ptr<WebURLResponse> response = std::move(preload_response_);
   ResourceResponse resource_response = response->ToResourceResponse();
   resource_response.SetEncodedDataLength(encoded_data_length);
@@ -188,6 +201,7 @@ DEFINE_TRACE(FetchEvent) {
   visitor->Trace(request_);
   visitor->Trace(preload_response_property_);
   ExtendableEvent::Trace(visitor);
+  ContextClient::Trace(visitor);
 }
 
 }  // namespace blink