fl_method_response.cc: fix lint failures (#21406)
fl_method_response.cc: fix lint failures (#21406)

Fix lint issues caused by `google-readability-braces-around-statements`.
Hixie/sky_engine,jason-simmons/flutter_engine,jason-simmons/sky_engine,jamesr/flutter_engine,chinmaygarde/sky_engine,rmacnak-google/engine,chinmaygarde/sky_engine,jason-simmons/flutter_engine,rmacnak-google/engine,chinmaygarde/sky_engine,jamesr/flutter_engine,jason-simmons/sky_engine,jamesr/flutter_engine,chinmaygarde/flutter_engine,devoncarew/engine,rmacnak-google/engine,aam/engine,devoncarew/sky_engine,aam/engine,jamesr/flutter_engine,chinmaygarde/sky_engine,rmacnak-google/engine,jamesr/flutter_engine,Hixie/sky_engine,jamesr/flutter_engine,devoncarew/sky_engine,chinmaygarde/flutter_engine,jamesr/sky_engine,chinmaygarde/flutter_engine,flutter/engine,rmacnak-google/engine,jason-simmons/sky_engine,aam/engine,devoncarew/sky_engine,aam/engine,rmacnak-google/engine,jason-simmons/sky_engine,chinmaygarde/flutter_engine,flutter/engine,chinmaygarde/flutter_engine,jamesr/flutter_engine,jason-simmons/flutter_engine,devoncarew/sky_engine,jamesr/sky_engine,jason-simmons/flutter_engine,jason-simmons/flutter_engine,jamesr/sky_engine,chinmaygarde/flutter_engine,flutter/engine,jamesr/flutter_engine,jason-simmons/sky_engine,jason-simmons/flutter_engine,Hixie/sky_engine,devoncarew/engine,Hixie/sky_engine,aam/engine,chinmaygarde/sky_engine,chinmaygarde/flutter_engine,flutter/engine,flutter/engine,Hixie/sky_engine,flutter/engine,rmacnak-google/engine,devoncarew/engine,devoncarew/engine,devoncarew/sky_engine,jamesr/sky_engine,jason-simmons/sky_engine,flutter/engine,aam/engine,devoncarew/engine,jamesr/sky_engine,chinmaygarde/sky_engine,Hixie/sky_engine,jamesr/sky_engine,chinmaygarde/sky_engine,aam/engine,devoncarew/sky_engine,devoncarew/engine,jason-simmons/flutter_engine,jason-simmons/flutter_engine,flutter/engine,devoncarew/sky_engine,jason-simmons/sky_engine,Hixie/sky_engine,jamesr/sky_engine,Hixie/sky_engine,devoncarew/engine,jamesr/flutter_engine,aam/engine