Fix strong mode errors in dart:io.

sdk/lib/io/websocket_impl.dart

Index: sdk/lib/io/websocket_impl.dart
diff --git a/sdk/lib/io/websocket_impl.dart b/sdk/lib/io/websocket_impl.dart
index 0972e84be2e3c547b7ee315470b94933f41ff392..206ec2f2ec6480942f4972403ba6769bc3b0448f 100644
--- a/sdk/lib/io/websocket_impl.dart
+++ b/sdk/lib/io/websocket_impl.dart
@@ -58,7 +58,8 @@ class _CompressionMaxWindowBits {
  * will lead to undefined behaviour.
  */
 // TODO(ajohnsen): make this transformer reusable?
-class _WebSocketProtocolTransformer implements StreamTransformer, EventSink {
+class _WebSocketProtocolTransformer
+    implements StreamTransformer, EventSink<Uint8List> {
   static const int START = 0;
   static const int LEN_FIRST = 1;
   static const int LEN_REST = 2;
@@ -996,6 +997,7 @@ class _WebSocketImpl extends Stream with _ServiceObject implements WebSocket {
 
       return request.close();
     }).then((response) {
+
       void error(String message) {
         // Flush data.
         response.detachSocket().then((socket) {
@@ -1003,6 +1005,7 @@ class _WebSocketImpl extends Stream with _ServiceObject implements WebSocket {
         });
         throw new WebSocketException(message);
       }
+
       if (response.statusCode != HttpStatus.SWITCHING_PROTOCOLS ||
           response.headers[HttpHeaders.CONNECTION] == null ||
           !response.headers[HttpHeaders.CONNECTION]
@@ -1032,7 +1035,7 @@ class _WebSocketImpl extends Stream with _ServiceObject implements WebSocket {
       _WebSocketPerMessageDeflate deflate =
           negotiateClientCompression(response, compression);
 
-      return response.detachSocket().then((socket) =>
+      return response.detachSocket().then/*<WebSocket>*/((socket) =>
           new _WebSocketImpl._fromSocket(
               socket, protocol, compression, false, deflate));
     });
@@ -1060,8 +1063,7 @@ class _WebSocketImpl extends Stream with _ServiceObject implements WebSocket {
           return DEFAULT_WINDOW_BITS;
         }
 
-        o = int.parse(o, onError: (s) => DEFAULT_WINDOW_BITS);
-        return o;
+        return int.parse(o, onError: (s) => DEFAULT_WINDOW_BITS);
       }
 
       return new _WebSocketPerMessageDeflate(
@@ -1216,9 +1218,9 @@ class _WebSocketImpl extends Stream with _ServiceObject implements WebSocket {
   String get _serviceTypePath => 'io/websockets';
   String get _serviceTypeName => 'WebSocket';
 
-  Map _toJSON(bool ref) {
+  Map<String, dynamic> _toJSON(bool ref) {
     var name = '${_socket.address.host}:${_socket.port}';
-    var r = {
+    var r = <String, dynamic>{
       'id': _servicePath,
       'type': _serviceType(ref),
       'name': name,