Don't send duplicate responses for debugger commands in Sky
Don't send duplicate responses for debugger commands in Sky

This fixes following error in DevTools front-end:
"Protocol Error: the message with wrong id. "
and makes breakpoint persist between debugging sessions.

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/746453002

iansf/sky_engine,jason-simmons/flutter_engine,krisgiesing/sky_engine,chinmaygarde/flutter_engine,devoncarew/sky_engine,krisgiesing/sky_engine,Hixie/sky_engine,zhangxq5012/sky_engine,jimsimon/sky_engine,mxia/engine,devoncarew/engine,mpcomplete/engine,xunmengfeng/engine,jamesr/flutter_engine,mpcomplete/flutter_engine,zhangxq5012/sky_engine,Hixie/sky_engine,takaaptech/sky_engine,Hixie/sky_engine,rmacnak-google/engine,aam/engine,cdotstout/sky_engine,Hixie/sky_engine,rmacnak-google/engine,mikejurka/engine,cdotstout/sky_engine,jimsimon/sky_engine,axinging/sky_engine,chinmaygarde/sky_engine,jamesr/flutter_engine,afandria/sky_engine,mikejurka/engine,axinging/sky_engine,chinmaygarde/sky_engine,zhangxq5012/sky_engine,mpcomplete/engine,devoncarew/sky_engine,axinging/sky_engine,lyceel/engine,aam/engine,cdotstout/sky_engine,jason-simmons/flutter_engine,devoncarew/engine,iansf/sky_engine,mpcomplete/engine,flutter/engine,TribeMedia/sky_engine,xunmengfeng/engine,aam/engine,tvolkert/engine,TribeMedia/sky_engine,Hixie/sky_engine,mxia/engine,takaaptech/sky_engine,mpcomplete/engine,afandria/sky_engine,mdakin/engine,abarth/sky_engine,jason-simmons/sky_engine,jamesr/sky_engine,jamesr/flutter_engine,flutter/engine,Hixie/sky_engine,cdotstout/sky_engine,mdakin/engine,tvolkert/engine,TribeMedia/sky_engine,afandria/sky_engine,chinmaygarde/flutter_engine,qiankunshe/sky_engine,Hixie/sky_engine,jamesr/sky_engine,tvolkert/engine,xunmengfeng/engine,axinging/sky_engine,jimsimon/sky_engine,afandria/sky_engine,jason-simmons/flutter_engine,zhangxq5012/sky_engine,jason-simmons/sky_engine,zhangxq5012/sky_engine,iansf/sky_engine,mpcomplete/flutter_engine,devoncarew/engine,jamesr/flutter_engine,chinmaygarde/sky_engine,rmacnak-google/engine,takaaptech/sky_engine,jason-simmons/sky_engine,takaaptech/sky_engine,jamesr/sky_engine,devoncarew/sky_engine,jason-simmons/flutter_engine,xunmengfeng/engine,qiankunshe/sky_engine,lyceel/engine,flutter/engine,mpcomplete/engine,TribeMedia/sky_engine,cdotstout/sky_engine,cdotstout/sky_engine,xunmengfeng/engine,aam/engine,mdakin/engine,jason-simmons/flutter_engine,jimsimon/sky_engine,jamesr/flutter_engine,lyceel/engine,axinging/sky_engine,jimsimon/sky_engine,devoncarew/engine,mdakin/engine,chinmaygarde/flutter_engine,devoncarew/sky_engine,chinmaygarde/flutter_engine,mikejurka/engine,lyceel/engine,abarth/sky_engine,abarth/sky_engine,iansf/sky_engine,zhangxq5012/sky_engine,mxia/engine,krisgiesing/sky_engine,jamesr/flutter_engine,TribeMedia/sky_engine,takaaptech/sky_engine,mdakin/engine,mdakin/engine,rmacnak-google/engine,iansf/sky_engine,lyceel/engine,afandria/sky_engine,TribeMedia/sky_engine,takaaptech/sky_engine,qiankunshe/sky_engine,afandria/sky_engine,flutter/engine,mpcomplete/engine,flutter/engine,mxia/engine,rmacnak-google/engine,takaaptech/sky_engine,axinging/sky_engine,takaaptech/sky_engine,mxia/engine,jimsimon/sky_engine,qiankunshe/sky_engine,mpcomplete/engine,mikejurka/engine,jason-simmons/flutter_engine,chinmaygarde/flutter_engine,mdakin/engine,rmacnak-google/engine,jamesr/sky_engine,tvolkert/engine,xunmengfeng/engine,TribeMedia/sky_engine,jamesr/flutter_engine,chinmaygarde/flutter_engine,devoncarew/engine,jason-simmons/sky_engine,krisgiesing/sky_engine,chinmaygarde/flutter_engine,chinmaygarde/sky_engine,mpcomplete/flutter_engine,mikejurka/engine,flutter/engine,TribeMedia/sky_engine,mpcomplete/flutter_engine,aam/engine,rmacnak-google/engine,TribeMedia/sky_engine,aam/engine,cdotstout/sky_engine,jamesr/flutter_engine,aam/engine,zhangxq5012/sky_engine,jimsimon/sky_engine,chinmaygarde/sky_engine,mikejurka/engine,mxia/engine,qiankunshe/sky_engine,abarth/sky_engine,mpcomplete/flutter_engine,devoncarew/sky_engine,jamesr/sky_engine,krisgiesing/sky_engine,devoncarew/engine,mxia/engine,jamesr/flutter_engine,zhangxq5012/sky_engine,abarth/sky_engine,iansf/sky_engine,devoncarew/engine,Hixie/sky_engine,mxia/engine,chinmaygarde/sky_engine,mpcomplete/engine,krisgiesing/sky_engine,mikejurka/engine,axinging/sky_engine,qiankunshe/sky_engine,krisgiesing/sky_engine,iansf/sky_engine,xunmengfeng/engine,mdakin/engine,tvolkert/engine,devoncarew/sky_engine,jimsimon/sky_engine,zhangxq5012/sky_engine,axinging/sky_engine,jamesr/sky_engine,jason-simmons/flutter_engine,qiankunshe/sky_engine,mpcomplete/flutter_engine,afandria/sky_engine,afandria/sky_engine,iansf/sky_engine,lyceel/engine,tvolkert/engine,devoncarew/sky_engine,tvolkert/engine,aam/engine,mikejurka/engine,jason-simmons/sky_engine,flutter/engine,axinging/sky_engine,abarth/sky_engine,flutter/engine,jimsimon/sky_engine,mikejurka/engine,chinmaygarde/sky_engine,jason-simmons/flutter_engine,qiankunshe/sky_engine,takaaptech/sky_engine,jason-simmons/sky_engine,jamesr/sky_engine,lyceel/engine,jason-simmons/sky_engine,abarth/sky_engine