message: Added experimental_flags to experimentally change the behavior of Japanese spellchecker.
  Added min_score(s) parameter. Suppress the suggestion of the score is less than min_score.
  Deprecated disable_model_bias parameter.
diff: @@ -854,10 +854,10 @@ message CheckSpellingRequest {
  // Used to control the precision/recall trade-off.
  optional float score_threshold = 2;
  - // Disables to add the special per-candidate bias-score stored in the model
  - // file. This flat should be enabled in experiment. We can make the behavior
  - // more aggressive.
  - optional bool disable_model_bias = 3;
  + reserved 3; // deprecated disable_model_bias
  +
  + // arbitrary experimental flags populated to spellchecker::Options.
  + repeated string experimental_flags = 4;
  }
  // Spellchecker response.
  