Add linter by default for polymer's pub-build, also cleans up the linter code.

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

Index: pkg/polymer/lib/src/build/build_filter.dart
diff --git a/pkg/polymer/lib/src/build/build_filter.dart b/pkg/polymer/lib/src/build/build_filter.dart
index 9bc8bd4fe0a7fbb14b4e506fd58b02255916cb55..fb62ca72e938fdacacd511073c786519293e7abb 100644
--- a/pkg/polymer/lib/src/build/build_filter.dart
+++ b/pkg/polymer/lib/src/build/build_filter.dart
@@ -44,4 +44,6 @@ class BuildFilter extends Transformer with PolymerTransformer {
       }
     });
   }
+
+  String toString() => 'polymer-build-filter';

[Siggi Cherem (dart-lang), 2013/12/12 03:14:55]

this is used by pub-build to indicate which transformer produced an
error/warning message.

[Jennifer Messerly, 2013/12/12 03:32:55]

nice!

My only question: should this just be '$runtimeType'? that way if we rename the
type the toString is updated for free. (and make the type called
'PolymerBuildFilter')

[Siggi Cherem (dart-lang), 2013/12/12 17:57:27]

haha - that's the default behavior from pub if you don't define 'toString'. But
I overwrote this to make it more user readable :-).

I prefer not to prefix every type just because it has a nicer print
representation, we can also just add "Polymer" in the toString.

The current messages look like this:

  [Warning in polymer-linter on sample|web/index.html]: ...
  [Warning in polymer-import-inliner on sample|web/index.html]: ...

Some other ideas:
- "Polymer$runtimeType"
  [Warning in PolymerLinter on sample|web/index.html]: ...
  [Warning in PolymerImportInliner on sample|web/index.html]: ...

- "polymer ($runtimeType)"
  [Warning in polymer (Linter) on sample|web/index.html]: ...
  [Warning in polymer (ImportInliner) on sample|web/index.html]: ...

I'm starting to like the last one the best. I just updated the CL to use that,
but will wait for your thoughts.

 }