Fix compilation errors in render-sector.dart
Fix compilation errors in render-sector.dart

TBR=abarth

Review URL: https://codereview.chromium.org/1153273002

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