Make FrameDestructionObserver::m_frame a private.

Source/core/plugins/DOMMimeType.h

Index: Source/core/plugins/DOMMimeType.h
diff --git a/Source/core/plugins/DOMMimeType.h b/Source/core/plugins/DOMMimeType.h
index 3833a2b01d2584df59b692492a9a7d8b838b337f..9d9fba223973079ef07ebf3bd56ba27c35fb03e1 100644
--- a/Source/core/plugins/DOMMimeType.h
+++ b/Source/core/plugins/DOMMimeType.h
@@ -52,9 +52,10 @@ public:
     virtual void trace(Visitor*) override;
 
 private:
+    DOMMimeType(PassRefPtr<PluginData>, LocalFrame*, unsigned index);
+
     const MimeClassInfo& mimeClassInfo() const { return m_pluginData->mimes()[m_index]; }
 
-    DOMMimeType(PassRefPtr<PluginData>, LocalFrame*, unsigned index);
     RefPtr<PluginData> m_pluginData;
     unsigned m_index;
 };