Add font substitution metric for Linux

pdf/preview_mode_client.h

 // Copyright (c) 2011 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 PDF_PREVIEW_MODE_CLIENT_H_
 #define PDF_PREVIEW_MODE_CLIENT_H_
 
 #include <stdint.h>
 
 #include <string>
@@ skipping 47 matching lines @@
   std::string ShowFileSelectionDialog() override;
   pp::URLLoader CreateURLLoader() override;
   void ScheduleCallback(int id, int delay_in_ms) override;
   void SearchString(const base::char16* string,
                     const base::char16* term,
                     bool case_sensitive,
                     std::vector<SearchStringResult>* results) override;
   void DocumentPaintOccurred() override;
   void DocumentLoadComplete(int page_count) override;
   void DocumentLoadFailed() override;
+  void FontSubstituted() override;
   pp::Instance* GetPluginInstance() override;
   void DocumentHasUnsupportedFeature(const std::string& feature) override;
   void DocumentLoadProgress(uint32_t available, uint32_t doc_size) override;
   void FormTextFieldFocusChange(bool in_focus) override;
   bool IsPrintPreview() override;
   uint32_t GetBackgroundColor() override;
 
  private:
   Client* const client_;
 };
 
 }  // namespace chrome_pdf
 
 #endif  // PDF_PREVIEW_MODE_CLIENT_H_