Fix obsolete `CronetClient()` constructor usage (#1042) #860

Job	Run time
mono_repo self validate	18s
analyze_and_format; Dart dev; PKGS: pkgs/http, pkgs/http_client_conformance_tests, pkgs/http_prof...	34s
analyze_and_format; Dart 2.19.0; PKG: pkgs/http_client_conformance_tests; `dart analyze --fatal-i...	29s
analyze_and_format; Dart 3.0.0; PKGS: pkgs/http, pkgs/http_profile; `dart analyze --fatal-infos`	21s
analyze_and_format; Dart dev; PKGS: pkgs/http, pkgs/http_client_conformance_tests, pkgs/http_prof...	29s
unit_test; Dart dev; PKG: pkgs/http; `dart run --define=no_default_http_client=true test/no_defau...	20s
unit_test; Dart 3.0.0; PKG: pkgs/http; `dart run --define=no_default_http_client=true test/no_def...	26s
unit_test; Dart 3.0.0; PKGS: pkgs/http, pkgs/http_profile; `dart test --platform vm`	1m 7s
unit_test; Dart 3.0.0; PKG: pkgs/http; `dart test --platform chrome`	1m 27s
unit_test; Dart dev; PKG: pkgs/http; `dart test --platform chrome`	2m 48s
unit_test; Dart dev; PKGS: pkgs/http, pkgs/http_profile; `dart test --platform vm`	1m 13s
	9m 32s

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