Add transformer support to Converters.

sdk/lib/convert/converter.dart

Index: sdk/lib/convert/converter.dart
diff --git a/sdk/lib/convert/converter.dart b/sdk/lib/convert/converter.dart
index bdc52626eb664b59366c8c146e10040018d9f1e8..5563d7c35c6565130e4c3b13ea7c440f2fe16b66 100644
--- a/sdk/lib/convert/converter.dart
+++ b/sdk/lib/convert/converter.dart
@@ -10,7 +10,7 @@ part of dart.convert;
  * *Converters are still experimental and are subject to change without notice.*
  *
  */
-abstract class Converter<S, T> {
+abstract class Converter<S, T> implements StreamTransformer {
   /**
    * Converts [input] and returns the result of the conversion.
    */
@@ -33,6 +33,11 @@ abstract class Converter<S, T> {
     throw new UnsupportedError(
         "This converter does not support chunked conversions: $this");
   }
+
+  // Subclasses are encouraged to provide better types.
+  Stream bind(Stream source) {
+    return new _ConverterTransformStream(source, this);
+  }
 }
 
 /**