core/loader: create private directory to store private classes

third_party/WebKit/Source/core/loader/FrameClientHintsPreferencesContext.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 FrameClientHintsPreferencesContext_h
-#define FrameClientHintsPreferencesContext_h
-
-#include "core/frame/Frame.h"
-#include "platform/heap/Persistent.h"
-#include "platform/loader/fetch/ClientHintsPreferences.h"
-#include "wtf/Allocator.h"
-
-namespace blink {
-
-class FrameClientHintsPreferencesContext final
-    : public ClientHintsPreferences::Context {
-  STACK_ALLOCATED();
-
- public:
-  explicit FrameClientHintsPreferencesContext(Frame*);
-
-  void countClientHintsDPR() override;
-  void countClientHintsResourceWidth() override;
-  void countClientHintsViewportWidth() override;
-
- private:
-  Member<Frame> m_frame;
-};
-
-}  // namespace blink
-
-#endif  // FrameClientHintsPreferencesContext_h