Restrict compilationQueue to library-visibility (#21280)
Restrict compilationQueue to library-visibility (#21280)

Its type uses a generic type which is limited to library-visibility.
Eliminating compilationQueue from ResidentCompiler's public interface
makes it possible to mock in tests.
tvolkert/flutter,tvolkert/flutter,tvolkert/flutter,Hixie/flutter,cbracken/flutter,Hixie/flutter,tvolkert/flutter,Hixie/flutter,cbracken/flutter,Hixie/flutter,flutter/flutter,Hixie/flutter,cbracken/flutter,flutter/flutter,cbracken/flutter,flutter/flutter,flutter/flutter,flutter/flutter,tvolkert/flutter,cbracken/flutter,flutter/flutter,flutter/flutter,Hixie/flutter,tvolkert/flutter,cbracken/flutter,cbracken/flutter,Hixie/flutter,flutter/flutter,flutter/flutter,flutter/flutter,cbracken/flutter,tvolkert/flutter,tvolkert/flutter,cbracken/flutter,tvolkert/flutter,Hixie/flutter,Hixie/flutter,Hixie/flutter,cbracken/flutter,tvolkert/flutter