Make only Flutter.framework files read-only (#8766)
Make only Flutter.framework files read-only (#8766)

Making the directories read-only causes problems with deletion, which
breaks the Mac chrome buildbot and DeviceLab.

Followup patch to cb2b89c38.
flutter/flutter,turnidge/flutter,Hixie/flutter,flutter/flutter,cbracken/flutter,tvolkert/flutter,Hixie/flutter,Hixie/flutter,tvolkert/flutter,tvolkert/flutter,cbracken/flutter,cbracken/flutter,cbracken/flutter,turnidge/flutter,tvolkert/flutter,tvolkert/flutter,Hixie/flutter,cbracken/flutter,turnidge/flutter,flutter/flutter,flutter/flutter,flutter/flutter,Hixie/flutter,Hixie/flutter,cbracken/flutter,turnidge/flutter,flutter/flutter,tvolkert/flutter,cbracken/flutter,cbracken/flutter,Hixie/flutter,cbracken/flutter,tvolkert/flutter,tvolkert/flutter,tvolkert/flutter,Hixie/flutter,flutter/flutter,Hixie/flutter,tvolkert/flutter,cbracken/flutter,turnidge/flutter,flutter/flutter,Hixie/flutter,flutter/flutter,flutter/flutter