Add --verbose flag to gn wrapper (#28318)
Add --verbose flag to gn wrapper (#28318)

When debugging gn invocations, it's useful to be able to run the
underlying `gn` tool in verbose mode. This adds a `--verbose` flag that
passes the `-v` flag on the underlying `gn` invocation.
flutter/engine,chinmaygarde/flutter_engine,jason-simmons/flutter_engine,jason-simmons/flutter_engine,rmacnak-google/engine,Hixie/sky_engine,aam/engine,rmacnak-google/engine,jason-simmons/flutter_engine,aam/engine,devoncarew/engine,rmacnak-google/engine,chinmaygarde/flutter_engine,jason-simmons/flutter_engine,devoncarew/engine,devoncarew/engine,flutter/engine,Hixie/sky_engine,jason-simmons/flutter_engine,jason-simmons/flutter_engine,Hixie/sky_engine,Hixie/sky_engine,aam/engine,chinmaygarde/flutter_engine,devoncarew/engine,jason-simmons/flutter_engine,devoncarew/engine,flutter/engine,aam/engine,aam/engine,rmacnak-google/engine,Hixie/sky_engine,rmacnak-google/engine,flutter/engine,Hixie/sky_engine,chinmaygarde/flutter_engine,aam/engine,devoncarew/engine,chinmaygarde/flutter_engine,flutter/engine,Hixie/sky_engine,aam/engine,jason-simmons/flutter_engine,flutter/engine,rmacnak-google/engine,aam/engine,flutter/engine,rmacnak-google/engine,flutter/engine,Hixie/sky_engine,devoncarew/engine,chinmaygarde/flutter_engine,chinmaygarde/flutter_engine