Switch transformers over to source_span

pkg/polymer/lib/src/build/common.dart

Index: pkg/polymer/lib/src/build/common.dart
diff --git a/pkg/polymer/lib/src/build/common.dart b/pkg/polymer/lib/src/build/common.dart
index 03c05bf6d56cd48b9b02f72c88c30e6ebb8015c8..dd70a223d53353ea93b2109776fb40986bfbde2a 100644
--- a/pkg/polymer/lib/src/build/common.dart
+++ b/pkg/polymer/lib/src/build/common.dart
@@ -16,7 +16,6 @@ import 'package:html5lib/dom.dart' show Document;
 import 'package:html5lib/parser.dart' show HtmlParser;
 import 'package:path/path.dart' as path;
 import 'package:observe/transformer.dart' show ObservableTransformer;
-import 'package:source_maps/span.dart' show Span;

[Siggi Cherem (dart-lang), 2014/07/29 23:41:37]

we probably need the equivalent import, otherwise the analyzer will complain
about the reference in the comment below. Alternatively, change the comment to
say source span in words

[nweiz, 2014/07/29 23:48:39]

I don't think the analyzer looks at references in doc comments.

[Siggi Cherem (dart-lang), 2014/07/30 00:00:06]

mmm - I think I got confused because it will not complain about an unused
warning when you use the symbol in a comment. 

Regardless, I guess it still matters for dart docs. I'm ok fixing it either way
(add import, or rewrite the actual comment)

[nweiz, 2014/07/30 00:25:53]

Done.

 
 const _ignoredErrors = const [
   'unexpected-dash-after-double-dash-in-comment',
@@ -125,7 +124,7 @@ abstract class PolymerTransformer {
   String toString() => 'polymer ($runtimeType)';
 }
 
-/// Gets the appropriate URL to use in a [Span] to produce messages
+/// Gets the appropriate URL to use in a [SourceSpan] to produce messages
 /// (e.g. warnings) for users. This will attempt to format the URL in the most
 /// useful way:
 ///