Implement direct write fallback proxy

content/child/dwrite_font_proxy/font_fallback_win.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 CONTENT_CHILD_DWRITE_FONT_PROXY_FONT_FALLBACK_WIN_H_
+#define CONTENT_CHILD_DWRITE_FONT_PROXY_FONT_FALLBACK_WIN_H_
+
+#include <dwrite.h>
+#include <dwrite_2.h>
+#include <wrl.h>
+
+#include "content/child/dwrite_font_proxy/dwrite_font_proxy_win.h"
+#include "content/common/content_export.h"
+#include "ipc/ipc_sender.h"
+
+namespace content {
+
+// Implements an  IDWriteFontFallback that uses IPC to proxy the fallback calls
+// to the system fallback in the browser process.
+class CONTENT_EXPORT FontFallback
+    : public Microsoft::WRL::RuntimeClass<
+          Microsoft::WRL::RuntimeClassFlags<Microsoft::WRL::ClassicCom>,
+          IDWriteFontFallback> {
+ public:
+  FontFallback();
+
+  HRESULT STDMETHODCALLTYPE
+  MapCharacters(IDWriteTextAnalysisSource* source,
+                UINT32 text_position,
+                UINT32 text_length,
+                IDWriteFontCollection* base_font_collection,
+                const wchar_t* base_family_name,
+                DWRITE_FONT_WEIGHT base_weight,
+                DWRITE_FONT_STYLE base_style,
+                DWRITE_FONT_STRETCH base_stretch,
+                UINT32* mapped_length,
+                IDWriteFont** mapped_font,
+                FLOAT* scale) override;
+
+  HRESULT STDMETHODCALLTYPE
+  RuntimeClassInitialize(DWriteFontCollectionProxy* collection,
+                         IPC::Sender* sender_override);
+
+ protected:
+  ~FontFallback() override;
+
+ private:
+  IPC::Sender* sender_override_;
+  Microsoft::WRL::ComPtr<DWriteFontCollectionProxy> collection_;
+
+  DISALLOW_ASSIGN(FontFallback);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_CHILD_DWRITE_FONT_PROXY_FONT_FALLBACK_WIN_H_