Add support for a "fine" barback log level.

pkg/barback/lib/src/transform_logger.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.transform_logger;
 
 import 'package:source_maps/span.dart';
 
 import 'asset_id.dart';
 import 'log.dart';
@@ skipping 11 matching lines @@
   /// Logs an informative message.
   ///
   /// If [asset] is provided, the log entry is associated with that asset.
   /// Otherwise it's associated with the primary input of [transformer].
   /// If [span] is provided, indicates the location in the input asset that
   /// caused the message.
   void info(String message, {AssetId asset, Span span}) {
     _logFunction(asset, LogLevel.INFO, message, span);
   }
 
+  /// Logs a message that won't be displayed unless the user is running in
+  /// verbose mode.
+  ///
+  /// If [asset] is provided, the log entry is associated with that asset.
+  /// Otherwise it's associated with the primary input of [transformer].
+  /// If [span] is provided, indicates the location in the input asset that
+  /// caused the message.
+  void fine(String message, {AssetId asset, Span span}) {
+    _logFunction(asset, LogLevel.FINE, message, span);
+  }
+
   /// Logs a warning message.
   ///
   /// If [asset] is provided, the log entry is associated with that asset.
   /// Otherwise it's associated with the primary input of [transformer].
   /// If present, [span] indicates the location in the input asset that caused
   /// the warning.
   void warning(String message, {AssetId asset, Span span}) {
     _logFunction(asset, LogLevel.WARNING, message, span);
   }
 
   /// Logs an error message.
   ///
   /// If [asset] is provided, the log entry is associated with that asset.
   /// Otherwise it's associated with the primary input of [transformer].
   /// If present, [span] indicates the location in the input asset that caused
   /// the error.
   // TODO(sigmund,nweiz): clarify when an error should be logged or thrown.
   void error(String message, {AssetId asset, Span span}) {
     _logFunction(asset, LogLevel.ERROR, message, span);
   }
 }