Introduce class Sink<T>.

sdk/lib/convert/ascii.dart

Index: sdk/lib/convert/ascii.dart
diff --git a/sdk/lib/convert/ascii.dart b/sdk/lib/convert/ascii.dart
index dcfed3878a99e4359344800a1525d3aec03806a4..b934556d01b59ee435d0351340f5a7b1f8c71547 100644
--- a/sdk/lib/convert/ascii.dart
+++ b/sdk/lib/convert/ascii.dart
@@ -93,8 +93,7 @@ class _UnicodeSubsetEncoder extends Converter<String, List<int>> {
    * The converter works more efficiently if the given [sink] is a
    * [ByteConversionSink].
    */
-  StringConversionSink startChunkedConversion(
-      ChunkedConversionSink<List<int>> sink) {
+  StringConversionSink startChunkedConversion(Sink<List<int>> sink) {
     if (sink is! ByteConversionSink) {
       sink = new ByteConversionSink.from(sink);
     }
@@ -204,8 +203,7 @@ abstract class _UnicodeSubsetDecoder extends Converter<List<int>, String> {
    * The converter works more efficiently if the given [sink] is a
    * [StringConversionSink].
    */
-  ByteConversionSink startChunkedConversion(
-      ChunkedConversionSink<String> sink) {
+  ByteConversionSink startChunkedConversion(Sink<String> sink) {
     StringConversionSink stringSink;
     if (sink is StringConversionSink) {
       stringSink = sink;
@@ -230,8 +228,7 @@ class AsciiDecoder extends _UnicodeSubsetDecoder {
    * The converter works more efficiently if the given [sink] is a
    * [StringConversionSink].
    */
-  ByteConversionSink startChunkedConversion(
-      ChunkedConversionSink<String> sink) {
+  ByteConversionSink startChunkedConversion(Sink<String> sink) {
     StringConversionSink stringSink;
     if (sink is StringConversionSink) {
       stringSink = sink;