Deleted OS_WIN and all Windows specific files from base.

base/win/iunknown_impl.h

-// Copyright (c) 2012 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 BASE_WIN_IUNKNOWN_IMPL_H_
-#define BASE_WIN_IUNKNOWN_IMPL_H_
-
-#include <unknwn.h>
-
-#include "base/atomic_ref_count.h"
-#include "base/base_export.h"
-#include "base/compiler_specific.h"
-
-namespace base {
-namespace win {
-
-// IUnknown implementation for other classes to derive from.
-class BASE_EXPORT IUnknownImpl : public IUnknown {
- public:
-  IUnknownImpl();
-
-  ULONG STDMETHODCALLTYPE AddRef() override;
-  ULONG STDMETHODCALLTYPE Release() override;
-
-  // Subclasses should extend this to return any interfaces they provide.
-  STDMETHODIMP QueryInterface(REFIID riid, void** ppv) override;
-
- protected:
-  virtual ~IUnknownImpl();
-
- private:
-  AtomicRefCount ref_count_;
-};
-
-}  // namespace win
-}  // namespace base
-
-#endif  // BASE_WIN_IUNKNOWN_IMPL_H_