Add the ability to dynamically modify transforms to barback.

sdk/lib/_internal/pub/lib/src/pub_package_provider.dart

Index: sdk/lib/_internal/pub/lib/src/pub_package_provider.dart
diff --git a/sdk/lib/_internal/pub/lib/src/pub_package_provider.dart b/sdk/lib/_internal/pub/lib/src/pub_package_provider.dart
index 0c4357196b9fba61453800d5b2b85fbbed2b611e..0e2c51b6f6a24eeaec9ae3c506febe16938afca0 100644
--- a/sdk/lib/_internal/pub/lib/src/pub_package_provider.dart
+++ b/sdk/lib/_internal/pub/lib/src/pub_package_provider.dart
@@ -46,9 +46,6 @@ class PubPackageProvider implements PackageProvider {
   /// Gets the root directory of [package].
   String getPackageDir(String package) => _packageDirs[package];
 
-  // TODO(rnystrom): Actually support transformers.
-  Iterable<Iterable<Transformer>> getTransformers(String package) => [];
-
   Future<Asset> getAsset(AssetId id) {
     var file = path.join(_packageDirs[id.package], id.path);
     return new Future.value(new Asset.fromPath(id, file));