Add support for a "fine" barback log level.

pkg/barback/lib/src/package_graph.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library barback.package_graph;
 
 import 'dart:async';
 
 import 'asset_cascade.dart';
 import 'asset_id.dart';
@@ skipping 66 matching lines @@
       // doesn't start building until some source in that graph is updated.
       _cascadeResults[package] = new BuildResult.success();
       _cascades[package] = cascade;
       cascade.onDirty.listen((_) {
         _cascadeResults[package] = null;
       });
 
       cascade.onLog.listen((entry) {
         if (_logController.hasListener) {
           _logController.add(entry);
-        } else {
+        } else if (entry.level != LogLevel.FINE) {
           // No listeners, so just print entry.
           var buffer = new StringBuffer();
           buffer.write("[${entry.level} ${entry.transform}] ");
 
           if (entry.span != null) {
             buffer.write(entry.span.getLocationMessage(entry.message));
           } else {
             buffer.write(entry.message);
           }
 
@@ skipping 93 matching lines @@
       if (cascade == null) throw new ArgumentError("Unknown package $package.");
       cascade.removeSources(ids);
     });
   }
 
   void updateTransformers(String package,
       Iterable<Iterable<Transformer>> transformers) {
     _cascades[package].updateTransformers(transformers);
   }
 }