Only support the new source_span spans in barback.

pkg/barback/lib/src/transformer/transform_logger.dart

Index: pkg/barback/lib/src/transformer/transform_logger.dart
diff --git a/pkg/barback/lib/src/transformer/transform_logger.dart b/pkg/barback/lib/src/transformer/transform_logger.dart
index 44ac420377cc93d80e7a6ddfbbf51077b8599258..5f26a9793f92f47d39806abe2e33407bf4d83a1d 100644
--- a/pkg/barback/lib/src/transformer/transform_logger.dart
+++ b/pkg/barback/lib/src/transformer/transform_logger.dart
@@ -4,15 +4,13 @@
 
 library barback.transformer.transform_logger;
 
-import 'package:source_maps/span.dart';
 import 'package:source_span/source_span.dart';
 
 import '../asset/asset_id.dart';
 import '../log.dart';
-import '../span_wrapper.dart';
 
 typedef void LogFunction(AssetId asset, LogLevel level, String message,
-                         Span span);
+                         SourceSpan span);
 
 /// Object used to report warnings and errors encountered while running a
 /// transformer.
@@ -26,10 +24,8 @@ class TransformLogger {
   /// 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. It may be a [SourceSpan] or a [Span], although the former is
-  /// recommended.
-  void info(String message, {AssetId asset, span}) {
-    if (span != null && span is SourceSpan) span = new SpanWrapper(span, false);
+  /// error.
+  void info(String message, {AssetId asset, SourceSpan span}) {
     _logFunction(asset, LogLevel.INFO, message, span);
   }
 
@@ -39,10 +35,8 @@ class TransformLogger {
   /// 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. It may be a [SourceSpan] or a [Span], although the former is
-  /// recommended.
-  void fine(String message, {AssetId asset, span}) {
-    if (span != null && span is SourceSpan) span = new SpanWrapper(span, false);
+  /// error.
+  void fine(String message, {AssetId asset, SourceSpan span}) {
     _logFunction(asset, LogLevel.FINE, message, span);
   }
 
@@ -51,10 +45,8 @@ class TransformLogger {
   /// 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. It may be a [SourceSpan] or a [Span], although the former is
-  /// recommended.
-  void warning(String message, {AssetId asset, span}) {
-    if (span != null && span is SourceSpan) span = new SpanWrapper(span, false);
+  /// error.
+  void warning(String message, {AssetId asset, SourceSpan span}) {
     _logFunction(asset, LogLevel.WARNING, message, span);
   }
 
@@ -63,8 +55,7 @@ class TransformLogger {
   /// 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. It may be a [SourceSpan] or a [Span], although the former is
-  /// recommended.
+  /// error.
   ///
   /// Logging any errors will cause Barback to consider the transformation to
   /// have failed, much like throwing an exception. This means that neither the
@@ -74,8 +65,7 @@ class TransformLogger {
   /// 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, span}) {
-    if (span != null && span is SourceSpan) span = new SpanWrapper(span, false);
+  void error(String message, {AssetId asset, SourceSpan span}) {
     _logFunction(asset, LogLevel.ERROR, message, span);
   }
 }