Have a Page's MemoryPurgeController be a separate allocation also.

Source/platform/MemoryPurgeController.h

 // Copyright 2015 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 MemoryPurgeController_h
 #define MemoryPurgeController_h
 
 #include "platform/PlatformExport.h"
 #include "platform/heap/Handle.h"
 #include "wtf/MainThread.h"
@@ skipping 23 matching lines @@
     // has occurred.
     virtual void purgeMemory(MemoryPurgeMode, DeviceKind) = 0;
 
     DECLARE_TRACE();
 };
 
 // MemoryPurgeController listens to some events which could be opportunities
 // for reducing memory consumption and notifies its clients.
 // Since we want to control memory per tab, MemoryPurgeController is owned by
 // Page.
-class PLATFORM_EXPORT MemoryPurgeController {
+class PLATFORM_EXPORT MemoryPurgeController final : public NoBaseWillBeGarbageCollected<MemoryPurgeController> {
+    DECLARE_EMPTY_DESTRUCTOR_WILL_BE_REMOVED(MemoryPurgeController);
 public:
-    MemoryPurgeController();
+    static PassOwnPtrWillBeRawPtr<MemoryPurgeController> create()
+    {
+        return adoptPtrWillBeNoop(new MemoryPurgeController);
+    }
 
     void registerClient(MemoryPurgeClient* client)
     {
         ASSERT(isMainThread());
         ASSERT(client);
         ASSERT(!m_clients.contains(client));
         m_clients.add(client);
     }
 
     void unregisterClient(MemoryPurgeClient* client)
     {
         ASSERT(isMainThread());
         ASSERT(m_clients.contains(client));
         m_clients.remove(client);
     }
 
     DECLARE_TRACE();
 
 private:
+    MemoryPurgeController();
+
     void purgeMemory(MemoryPurgeMode);
 
     WillBeHeapHashSet<RawPtrWillBeWeakMember<MemoryPurgeClient>> m_clients;
     DeviceKind m_deviceKind;
 };
 
 } // namespace blink
 
 #endif // MemoryPurgeController_h