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

Source/platform/MemoryPurgeController.cpp

 // 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.
 
 #include "config.h"
 #include "platform/MemoryPurgeController.h"
 
 #include "public/platform/Platform.h"
 
 namespace blink {
 
 MemoryPurgeController::MemoryPurgeController()
     : m_deviceKind(Platform::current()->isLowEndDeviceMode() ? DeviceKind::LowEnd : DeviceKind::NotSpecified)
 {
 }
 
+DEFINE_EMPTY_DESTRUCTOR_WILL_BE_REMOVED(MemoryPurgeController);
+
 void MemoryPurgeController::purgeMemory(MemoryPurgeMode purgeMode)
 {
     for (auto& client : m_clients)
         client->purgeMemory(purgeMode, m_deviceKind);
 }
 
 DEFINE_TRACE(MemoryPurgeController)
 {
 #if ENABLE(OILPAN)
     visitor->trace(m_clients);
 #endif
 }
 
 } // namespace blink