Fix analyzer warning. (#4715)
Fix analyzer warning. (#4715)

* Fix analyzer warning.

  warning • This function declares a return type of 'Future<void>', but doesn't end with a return statement at flutter/frontend_server/lib/server.dart:340:1 • missing_return

* Remove await

* Ignore warning.

flutter/engine,Hixie/sky_engine,mikejurka/engine,Hixie/sky_engine,mikejurka/engine,Hixie/sky_engine,jamesr/flutter_engine,flutter/engine,jason-simmons/sky_engine,Hixie/sky_engine,krisgiesing/sky_engine,rmacnak-google/engine,chinmaygarde/sky_engine,aam/engine,jason-simmons/flutter_engine,chinmaygarde/sky_engine,chinmaygarde/sky_engine,devoncarew/engine,jamesr/sky_engine,chinmaygarde/flutter_engine,jamesr/sky_engine,chinmaygarde/sky_engine,tvolkert/engine,krisgiesing/sky_engine,mikejurka/engine,cdotstout/sky_engine,jason-simmons/flutter_engine,devoncarew/engine,cdotstout/sky_engine,devoncarew/sky_engine,devoncarew/engine,jason-simmons/sky_engine,jamesr/flutter_engine,flutter/engine,jamesr/sky_engine,Hixie/sky_engine,tvolkert/engine,jason-simmons/flutter_engine,jason-simmons/flutter_engine,mikejurka/engine,cdotstout/sky_engine,mikejurka/engine,flutter/engine,devoncarew/engine,chinmaygarde/sky_engine,cdotstout/sky_engine,chinmaygarde/flutter_engine,jason-simmons/flutter_engine,chinmaygarde/flutter_engine,rmacnak-google/engine,jamesr/sky_engine,mikejurka/engine,flutter/engine,jamesr/flutter_engine,tvolkert/engine,tvolkert/engine,cdotstout/sky_engine,chinmaygarde/sky_engine,Hixie/sky_engine,devoncarew/engine,aam/engine,mikejurka/engine,flutter/engine,krisgiesing/sky_engine,devoncarew/sky_engine,flutter/engine,cdotstout/sky_engine,devoncarew/sky_engine,jason-simmons/flutter_engine,rmacnak-google/engine,flutter/engine,devoncarew/sky_engine,aam/engine,rmacnak-google/engine,aam/engine,krisgiesing/sky_engine,chinmaygarde/flutter_engine,krisgiesing/sky_engine,krisgiesing/sky_engine,jamesr/flutter_engine,chinmaygarde/sky_engine,jamesr/flutter_engine,krisgiesing/sky_engine,jamesr/sky_engine,devoncarew/sky_engine,jason-simmons/flutter_engine,devoncarew/engine,rmacnak-google/engine,aam/engine,jamesr/flutter_engine,jamesr/flutter_engine,rmacnak-google/engine,Hixie/sky_engine,devoncarew/sky_engine,jason-simmons/sky_engine,tvolkert/engine,jason-simmons/flutter_engine,chinmaygarde/flutter_engine,cdotstout/sky_engine,jamesr/flutter_engine,chinmaygarde/flutter_engine,mikejurka/engine,jason-simmons/sky_engine,jamesr/flutter_engine,aam/engine,jamesr/sky_engine,jamesr/sky_engine,mikejurka/engine,tvolkert/engine,rmacnak-google/engine,jason-simmons/sky_engine,devoncarew/engine,jason-simmons/sky_engine,aam/engine,tvolkert/engine,jason-simmons/sky_engine,devoncarew/sky_engine,Hixie/sky_engine,aam/engine,chinmaygarde/flutter_engine