Web benchmarks: make headless mode opt-out (#50166)
Web benchmarks: make headless mode opt-out (#50166)


tvolkert/flutter,cbracken/flutter,cbracken/flutter,cbracken/flutter,flutter/flutter,flutter/flutter,Hixie/flutter,Hixie/flutter,cbracken/flutter,Hixie/flutter,cbracken/flutter,Hixie/flutter,Hixie/flutter,tvolkert/flutter,tvolkert/flutter,tvolkert/flutter,tvolkert/flutter,flutter/flutter,Hixie/flutter,Hixie/flutter,cbracken/flutter,Hixie/flutter,cbracken/flutter,cbracken/flutter,tvolkert/flutter,flutter/flutter,cbracken/flutter,tvolkert/flutter,Hixie/flutter,tvolkert/flutter,flutter/flutter,flutter/flutter,tvolkert/flutter,flutter/flutter,Hixie/flutter,flutter/flutter,flutter/flutter,tvolkert/flutter,flutter/flutter,cbracken/flutter