Add a .analysis_options file.
Add a .analysis_options file.

R=rnystrom@google.com

Review URL: https://codereview.chromium.org//1919073002 .

dart-lang/http,dart-lang/http,dart-lang/http,dart-lang/http,donny-dont/http,dart-lang/http,dart-lang/http,dart-lang/http,dart-lang/http