Remove deprecated CollectionSink and Stream.pipeInto.

pkg/http/lib/src/multipart_request.dart

Index: pkg/http/lib/src/multipart_request.dart
diff --git a/pkg/http/lib/src/multipart_request.dart b/pkg/http/lib/src/multipart_request.dart
index bc588713cf61d0bd2c4b4654e675bb5da6bbb583..bebc552fd3bfdf165b23b94cc9a9856e3b67a0d7 100644
--- a/pkg/http/lib/src/multipart_request.dart
+++ b/pkg/http/lib/src/multipart_request.dart
@@ -52,7 +52,7 @@ class MultipartRequest extends BaseRequest {
           encodeUtf8(value).length + "\r\n".length;
     });
 
-    for (var file in _files.collection) {
+    for (var file in _files) {
       length += "--".length + _BOUNDARY_LENGTH + "\r\n".length +
           _headerForFile(file).length +
           file.length + "\r\n".length;
@@ -73,17 +73,16 @@ class MultipartRequest extends BaseRequest {
   ///
   /// This doesn't need to be closed. When the request is sent, whichever files
   /// are written to this sink at that point will be used.
-  CollectionSink<MultipartFile> get files => _files;
+  List<MultipartFile> get files => _files;
 
-  /// The private version of [files], typed so that the underlying collection is
-  /// accessible.
-  final CollectionSink<MultipartFile> _files;
+  /// The private version of [files].
+  final List<MultipartFile> _files;
 
   /// Creates a new [MultipartRequest].
   MultipartRequest(String method, Uri url)
     : super(method, url),
       fields = {},
-      _files = new CollectionSink<MultipartFile>(<MultipartFile>[]);
+      _files = <MultipartFile>[];
 
   /// Freezes all mutable fields and returns a single-subscription [ByteStream]
   /// that will emit the request body.
@@ -111,7 +110,7 @@ class MultipartRequest extends BaseRequest {
       writeLine();
     });
 
-    Future.forEach(_files.collection, (file) {
+    Future.forEach(_files, (file) {
       writeAscii('--$boundary\r\n');
       writeAscii(_headerForFile(file));
       return writeStreamToSink(file.finalize(), controller)