Do not initiate fetch() on a destroyed FetchManager.

third_party/WebKit/Source/modules/fetch/GlobalFetch.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "modules/fetch/GlobalFetch.h"
 
 #include "core/frame/LocalDOMWindow.h"
 #include "core/frame/UseCounter.h"
 #include "core/inspector/InspectorInstrumentation.h"
 #include "core/workers/WorkerGlobalScope.h"
@@ skipping 22 matching lines @@
       supplement = new GlobalFetchImpl(executionContext);
       Supplement<T>::provideTo(supplementable, supplementName(), supplement);
     }
     return supplement;
   }
 
   ScriptPromise fetch(ScriptState* scriptState,
                       const RequestInfo& input,
                       const Dictionary& init,
                       ExceptionState& exceptionState) override {
-    if (!scriptState->contextIsValid()) {
+    ExecutionContext* executionContext = m_fetchManager->getExecutionContext();
+    if (!scriptState->contextIsValid() || !executionContext) {
       // TODO(yhirano): Should this be moved to bindings?
       exceptionState.throwTypeError("The global scope is shutting down.");
       return ScriptPromise();
     }
 
     // "Let |r| be the associated request of the result of invoking the
     // initial value of Request as constructor with |input| and |init| as
     // arguments. If this throws an exception, reject |p| with it."
     Request* r = Request::create(scriptState, input, init, exceptionState);
     if (exceptionState.hadException())
       return ScriptPromise();
 
-    if (ExecutionContext* executionContext =
-            m_fetchManager->getExecutionContext())
-      InspectorInstrumentation::willSendXMLHttpOrFetchNetworkRequest(
-          executionContext, r->url());
+    InspectorInstrumentation::willSendXMLHttpOrFetchNetworkRequest(
+        executionContext, r->url());
     return m_fetchManager->fetch(scriptState, r->passRequestData(scriptState));
   }
 
   DEFINE_INLINE_VIRTUAL_TRACE() {
     visitor->trace(m_fetchManager);
     ScopedFetcher::trace(visitor);
     Supplement<T>::trace(visitor);
   }
 
  private:
@@ skipping 38 matching lines @@
                                  const RequestInfo& input,
                                  const Dictionary& init,
                                  ExceptionState& exceptionState) {
   // Note that UseCounter doesn't work with SharedWorker or ServiceWorker.
   UseCounter::count(worker.getExecutionContext(), UseCounter::Fetch);
   return ScopedFetcher::from(worker)->fetch(scriptState, input, init,
                                             exceptionState);
 }
 
 }  // namespace blink