Make FrameDestructionObserver::m_frame a private.

Source/core/plugins/DOMMimeType.cpp

 /*
  *  Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
  *
  *  This library is free software; you can redistribute it and/or
  *  modify it under the terms of the GNU Lesser General Public
  *  License as published by the Free Software Foundation; either
  *  version 2 of the License, or (at your option) any later version.
  *
  *  This library is distributed in the hope that it will be useful,
  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 52 matching lines @@
 
 const String &DOMMimeType::description() const
 {
     return mimeClassInfo().desc;
 }
 
 PassRefPtrWillBeRawPtr<DOMPlugin> DOMMimeType::enabledPlugin() const
 {
     // FIXME: allowPlugins is just a client call. We should not need
     // to bounce through the loader to get there.
-    // Something like: m_frame->host()->client()->allowPlugins().
-    if (!m_frame || !m_frame->loader().allowPlugins(NotAboutToInstantiatePlugin))
+    // Something like: frame()->host()->client()->allowPlugins().
+    if (!frame() || !frame()->loader().allowPlugins(NotAboutToInstantiatePlugin))
         return nullptr;
 
-    return DOMPlugin::create(m_pluginData.get(), m_frame, m_pluginData->mimePluginIndices()[m_index]);
+    return DOMPlugin::create(m_pluginData.get(), frame(), m_pluginData->mimePluginIndices()[m_index]);
 }
 
 } // namespace blink