anchor.diff:        ${mkPluginInfo {
           output = "widevine";
           flags = [ "--register-pepper-plugins=${wvModule}${wvInfo}" ];
  -        envVars.NIX_CHROMIUM_PLUGIN_PATH_WIDEVINE = "$widevine/lib";
  +        envVars.NIX_CHROMIUM_PLUGIN_PATH_WIDEVINE = "@widevine@/lib";
         }}
       '';
   
  
positive.code:   mkPluginInfo = { output ? "out", allowedVars ? [ output ]
                   , flags ? [], envVars ? {}
                   }: let
      shSearch = ["'"] ++ map (var: "\$${var}") allowedVars;
      shReplace = ["'\\''"] ++ map (var: "'\"\${${var}}\"'") allowedVars;
      # We need to triple-escape "val":
      #  * First because makeWrapper doesn't do any quoting of its arguments by
  
negative.code:         output = "flash";
          allowedVars = [ "flash" "flashVersion" ];
          flags = [
            "--ppapi-flash-path=@flash@/lib/libpepflashplayer.so"
            "--ppapi-flash-version=@flashVersion@"
          ];
        }}
  
  