Add observatory_pub_packages snapshot to third_party

observatory_pub_packages/barback/src/transformer/transform_logger.dart

Index: observatory_pub_packages/barback/src/transformer/transform_logger.dart
===================================================================
--- observatory_pub_packages/barback/src/transformer/transform_logger.dart	(revision 0)
+++ observatory_pub_packages/barback/src/transformer/transform_logger.dart	(working copy)
@@ -0,0 +1,71 @@
+// 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.transformer.transform_logger;
+
+import 'package:source_span/source_span.dart';
+
+import '../asset/asset_id.dart';
+import '../log.dart';
+
+typedef void LogFunction(AssetId asset, LogLevel level, String message,
+                         SourceSpan span);
+
+/// Object used to report warnings and errors encountered while running a
+/// transformer.
+class TransformLogger {
+  final LogFunction _logFunction;
+
+  TransformLogger(this._logFunction);
+
+  /// 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
+  /// present, [span] indicates the location in the input asset that caused the
+  /// error.
+  void info(String message, {AssetId asset, SourceSpan 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
+  /// present, [span] indicates the location in the input asset that caused the
+  /// error.
+  void fine(String message, {AssetId asset, SourceSpan 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
+  /// error.
+  void warning(String message, {AssetId asset, SourceSpan 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.
+  ///
+  /// Logging any errors will cause Barback to consider the transformation to
+  /// have failed, much like throwing an exception. This means that neither the
+  /// primary input nor any outputs emitted by the transformer will be passed on
+  /// to the following phase, and the build will be reported as having failed.
+  ///
+  /// Unlike throwing an exception, this doesn't cause a transformer to stop
+  /// running. This makes it useful in cases where a single input may have
+  /// multiple errors that the user wants to know about.
+  void error(String message, {AssetId asset, SourceSpan span}) {
+    _logFunction(asset, LogLevel.ERROR, message, span);
+  }
+}