Add font failure telemetry

content/browser/renderer_host/dwrite_font_proxy_message_filter_win.h

Index: content/browser/renderer_host/dwrite_font_proxy_message_filter_win.h
diff --git a/content/browser/renderer_host/dwrite_font_proxy_message_filter_win.h b/content/browser/renderer_host/dwrite_font_proxy_message_filter_win.h
index c105f4d07687812672c0981a298a2ec4c24c5a20..7539ff16f6b4a9a22b48b0a4a944747efa672f99 100644
--- a/content/browser/renderer_host/dwrite_font_proxy_message_filter_win.h
+++ b/content/browser/renderer_host/dwrite_font_proxy_message_filter_win.h
@@ -62,6 +62,8 @@ class CONTENT_EXPORT DWriteFontProxyMessageFilter
                     IDWriteLocalFontFileLoader* local_loader,
                     IDWriteFontFile* font_file);
 
+  bool IsLastResortFallbackFont(uint32_t font_index);
+
  private:
   bool direct_write_initialized_ = false;
   Microsoft::WRL::ComPtr<IDWriteFontCollection> collection_;
@@ -69,6 +71,9 @@ class CONTENT_EXPORT DWriteFontProxyMessageFilter
   Microsoft::WRL::ComPtr<IDWriteFontFallback> font_fallback_;
   base::string16 windows_fonts_path_;
 
+  // Temp code to help track down crbug.com/561873
+  std::vector<uint32_t> last_resort_fonts_;
+
   DISALLOW_COPY_AND_ASSIGN(DWriteFontProxyMessageFilter);
 };