Prefer ContextClient mixin over manual ExecutionContext handling.

third_party/WebKit/Source/modules/presentation/PresentationConnectionList.h

 // Copyright 2016 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.
 
 #ifndef PresentationConnectionList_h
 #define PresentationConnectionList_h
 
+#include "core/dom/ExecutionContext.h"
 #include "core/events/EventTarget.h"
 #include "modules/ModulesExport.h"
 #include "modules/presentation/PresentationConnection.h"
 #include "platform/heap/Handle.h"
-#include "platform/heap/Heap.h"
 
 namespace blink {
 
 // Implements the PresentationConnectionList interface from the Presentation API
 // from which represents set of presentation connections in the set of
 // presentation controllers.
 class MODULES_EXPORT PresentationConnectionList final
-    : public EventTargetWithInlineData {
+    : public EventTargetWithInlineData,
+      public ContextClient {
   DEFINE_WRAPPERTYPEINFO();
+  USING_GARBAGE_COLLECTED_MIXIN(PresentationConnectionList);
 
  public:
   explicit PresentationConnectionList(ExecutionContext*);
   ~PresentationConnectionList() = default;
 
   // EventTarget implementation.
   const AtomicString& interfaceName() const override;
   ExecutionContext* getExecutionContext() const override {
-    return m_executionContext;
+    return ContextClient::getExecutionContext();
   }
 
   // PresentationConnectionList.idl implementation.
   const HeapVector<Member<PresentationConnection>>& connections() const;
   DEFINE_ATTRIBUTE_EVENT_LISTENER(connectionavailable);
 
   void addConnection(PresentationConnection*);
   void dispatchConnectionAvailableEvent(PresentationConnection*);
   bool isEmpty();
 
   DECLARE_VIRTUAL_TRACE();
 
  protected:
   // EventTarget implementation.
   void addedEventListener(const AtomicString& eventType,
                           RegisteredEventListener&) override;
 
  private:
   friend class PresentationReceiverTest;
 
   HeapVector<Member<PresentationConnection>> m_connections;
-  Member<ExecutionContext> m_executionContext;
 };
 
 }  // namespace blink
 
 #endif  // PresentationConnectionList_h