Reduce logging of setLibraryDebuggable
Reduce logging of setLibraryDebuggable

Can be reverted when https://github.com/dart-lang/webdev/issues/606 is done.

Dart-Code/Dart-Code,Dart-Code/Dart-Code,Dart-Code/Dart-Code,Dart-Code/Dart-Code,Dart-Code/Dart-Code