Extract the Skia implementation of HarfBuzz font to its own file

ui/gfx/harfbuzz_font_skia.h

+// 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.
+
+#ifndef UI_GFX_HARFBUZZ_FONT_SKIA_H_
+#define UI_GFX_HARFBUZZ_FONT_SKIA_H_
+
+#include "third_party/harfbuzz-ng/src/hb.h"
+#include "third_party/skia/include/core/SkScalar.h"
+#include "ui/gfx/font_render_params.h"
+
+class SkTypeface;
+
+namespace gfx {
+
+hb_font_t* CreateHarfBuzzFont(SkTypeface* skia_face,
+                              SkScalar text_size,
+                              const FontRenderParams& params,
+                              bool background_is_transparent);
+
+}  // namespace gfx
+
+#endif  // UI_GFX_HARFBUZZ_FONT_SKIA_H_