Implement fallback cache

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 <list>
+#include <map>
+
 #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<
@@ skipping 15 matching lines @@
                 IDWriteFont** mapped_font,
                 FLOAT* scale) override;
 
   HRESULT STDMETHODCALLTYPE
   RuntimeClassInitialize(DWriteFontCollectionProxy* collection,
                          IPC::Sender* sender_override);
 
  protected:
   ~FontFallback() override;
 
+  bool GetCachedFont(const base::string16& text,
+                     const wchar_t* base_family_name,
+                     DWRITE_FONT_WEIGHT base_weight,
+                     DWRITE_FONT_STYLE base_style,
+                     DWRITE_FONT_STRETCH base_stretch,
+                     IDWriteFont** mapped_font,
+                     uint32_t* mapped_length);
+
+  void AddCachedFamily(Microsoft::WRL::ComPtr<IDWriteFontFamily> family,
+                       const wchar_t* base_family_name);
+
  private:
   IPC::Sender* sender_override_;
   Microsoft::WRL::ComPtr<DWriteFontCollectionProxy> collection_;
 
+  // |fallback_family_cache_| keeps a mapping from base family name to a list
+  // of font families that matched a character on a previous call. The list is
+  // capped in size and maintained in MRU order. This gives us a good chance of
+  // returning a suitable fallback font without having to do an IPC.
+  std::map<base::string16, std::list<Microsoft::WRL::ComPtr<IDWriteFontFamily>>>
+      fallback_family_cache_;
+
   DISALLOW_ASSIGN(FontFallback);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_CHILD_DWRITE_FONT_PROXY_FONT_FALLBACK_WIN_H_