Add FontFaceSource interface and make it available on Document

third_party/WebKit/Source/core/css/FontFaceSource.h

+// Copyright 2017 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 FontFaceSource_h
+#define FontFaceSource_h
+
+#include "platform/heap/Handle.h"
+#include "platform/wtf/Allocator.h"
+#include "platform/wtf/PassRefPtr.h"
+
+namespace blink {
+
+class Document;
+class FontFaceSet;
+
+class FontFaceSource {
+  STATIC_ONLY(FontFaceSource);
+
+ public:
+  static FontFaceSet* fonts(Document&);
+};
+
+}  // namespace blink
+
+#endif  // FontFaceSource_h