Revert "Remove Sink and move CollectionSink to async."

sdk/lib/_internal/compiler/implementation/dart2js.dart

Index: sdk/lib/_internal/compiler/implementation/dart2js.dart
diff --git a/sdk/lib/_internal/compiler/implementation/dart2js.dart b/sdk/lib/_internal/compiler/implementation/dart2js.dart
index a2a4c37235982059f048b9c82b3f72ec977b2f71..d66579f6b6d5b0a941fa87e2c60a1d39f9814bf0 100644
--- a/sdk/lib/_internal/compiler/implementation/dart2js.dart
+++ b/sdk/lib/_internal/compiler/implementation/dart2js.dart
@@ -263,7 +263,7 @@ void compile(List<String> argv) {
     }
   }
 
-  StreamSink<String> outputProvider(String name, String extension) {
+  Sink<String> outputProvider(String name, String extension) {
     Uri uri;
     String sourceMapFileName;
     bool isPrimaryOutput = false;
@@ -314,8 +314,8 @@ void compile(List<String> argv) {
 }
 
 // TODO(ahe): Get rid of this class if http://dartbug.com/8118 is fixed.
-class CountingSink implements StreamSink<String> {
-  final StreamSink<String> sink;
+class CountingSink implements Sink<String> {
+  final Sink<String> sink;
   int count = 0;
 
   CountingSink(this.sink);
@@ -325,8 +325,6 @@ class CountingSink implements StreamSink<String> {
     count += value.length;
   }
 
-  signalError(AsyncError error) => sink.signalError(error);
-
   close() => sink.close();
 }