only perform multi-root mapping if there are multiple roots (#28352)
only perform multi-root mapping if there are multiple roots (#28352)


Hixie/flutter,flutter/flutter,flutter/flutter,Hixie/flutter,cbracken/flutter,tvolkert/flutter,cbracken/flutter,flutter/flutter,flutter/flutter,Hixie/flutter,cbracken/flutter,Hixie/flutter,flutter/flutter,tvolkert/flutter,cbracken/flutter,tvolkert/flutter,cbracken/flutter,cbracken/flutter,tvolkert/flutter,flutter/flutter,flutter/flutter,flutter/flutter,tvolkert/flutter,cbracken/flutter,Hixie/flutter,tvolkert/flutter,Hixie/flutter,tvolkert/flutter,cbracken/flutter,flutter/flutter,Hixie/flutter,tvolkert/flutter,tvolkert/flutter,cbracken/flutter,flutter/flutter,Hixie/flutter,Hixie/flutter,cbracken/flutter,Hixie/flutter,tvolkert/flutter