Allow spaces in SDK path in flutter_tools tests (#14617)
Allow spaces in SDK path in flutter_tools tests (#14617)

The Flutter engine now supports package: and file: imports that resolve
to paths on disk that include spaces and other URI-escaped characters.
This patch eliminates the restriction that Dart source paths not include
%20 (or other URI-escaped characters) in their paths in flutter_tool
tests.
cbracken/flutter,flutter/flutter,Hixie/flutter,tvolkert/flutter,flutter/flutter,cbracken/flutter,Hixie/flutter,cbracken/flutter,tvolkert/flutter,tvolkert/flutter,cbracken/flutter,flutter/flutter,tvolkert/flutter,Hixie/flutter,tvolkert/flutter,flutter/flutter,cbracken/flutter,tvolkert/flutter,Hixie/flutter,Hixie/flutter,tvolkert/flutter,Hixie/flutter,flutter/flutter,tvolkert/flutter,Hixie/flutter,tvolkert/flutter,cbracken/flutter,Hixie/flutter,cbracken/flutter,cbracken/flutter,cbracken/flutter,flutter/flutter,flutter/flutter,flutter/flutter,cbracken/flutter,Hixie/flutter,flutter/flutter,Hixie/flutter,tvolkert/flutter,flutter/flutter