linux: handle basic metric-compatibile font fallback

skia/ext/SkFontHost_fontconfig_direct.h

Index: skia/ext/SkFontHost_fontconfig_direct.h
diff --git a/skia/ext/SkFontHost_fontconfig_direct.h b/skia/ext/SkFontHost_fontconfig_direct.h
index 56bea34873f260cdae8beb7800134effa322dc1d..3f9475d05bb01c2cf25d58aef5e400237b189be6 100644
--- a/skia/ext/SkFontHost_fontconfig_direct.h
+++ b/skia/ext/SkFontHost_fontconfig_direct.h
@@ -35,6 +35,10 @@ class FontConfigDirect : public FontConfigInterface {
     virtual int Open(unsigned fileid);
 
   private:
+    // Return true if font_a and font_b are completely interchangeable;
+    // e.g., there exist free clones of certain well-known fonts.
+    bool IsMetricCompatibleReplacement(const char* font_a, const char* font_b);
+
     SkMutex mutex_;
     std::map<unsigned, std::string> fileid_to_filename_;
     std::map<std::string, unsigned> filename_to_fileid_;