Remove unneeded import and fix analyzer warnings
Remove unneeded import and fix analyzer warnings

R=ianh@google.com, hixie

Review URL: https://codereview.chromium.org/1190573002.

tvolkert/flutter,aghassemi/flutter,jason-simmons/flutter,cbracken/flutter,flutter/flutter,cbracken/flutter,tvolkert/flutter,cbracken/flutter,jason-simmons/flutter,flutter/flutter,Hixie/flutter,flutter/flutter,aghassemi/flutter,Hixie/flutter,Hixie/flutter,cbracken/flutter,cbracken/flutter,tvolkert/flutter,flutter/flutter,turnidge/flutter,tvolkert/flutter,cbracken/flutter,tvolkert/flutter,cbracken/flutter,tvolkert/flutter,flutter/flutter,turnidge/flutter,tvolkert/flutter,Hixie/flutter,cbracken/flutter,jason-simmons/flutter,cbracken/flutter,Hixie/flutter,aghassemi/flutter,Hixie/flutter,tvolkert/flutter,cbracken/flutter,turnidge/flutter,flutter/flutter,turnidge/flutter,tvolkert/flutter,Hixie/flutter,tvolkert/flutter,flutter/flutter,Hixie/flutter,aghassemi/flutter,flutter/flutter,flutter/flutter,turnidge/flutter,jason-simmons/flutter,Hixie/flutter,flutter/flutter,Hixie/flutter