Fix type warnings and remove unimplemented stuff from HttpClient interface.

sdk/lib/io/http_impl.dart

Index: sdk/lib/io/http_impl.dart
diff --git a/sdk/lib/io/http_impl.dart b/sdk/lib/io/http_impl.dart
index 4f65b855d04ecb9cd8cb3d10a5d41f9d11b034f7..349794d327ef208fd6f2e0b559454ba2d18255a1 100644
--- a/sdk/lib/io/http_impl.dart
+++ b/sdk/lib/io/http_impl.dart
@@ -314,7 +314,7 @@ class _HttpClientResponse
 }
 
 
-class _HttpOutboundMessage<T> extends IOSink {
+abstract class _HttpOutboundMessage<T> extends IOSink {
   // Used to mark when the body should be written. This is used for HEAD
   // requests and in error handling.
   bool _ignoreBody = false;
@@ -330,7 +330,7 @@ class _HttpOutboundMessage<T> extends IOSink {
   }
 
   bool get persistentConnection => headers.persistentConnection;
-  bool set persistentConnection(bool p) {
+  void set persistentConnection(bool p) {
     headers.persistentConnection = p;
   }
 
@@ -1062,7 +1062,7 @@ class _HttpClient implements HttpClient {
   Future<HttpClientRequest> _openUrlFromRequest(String method,
                                                 Uri uri,
                                                 _HttpClientRequest previous) {
-    return openUrl(method, uri).then((request) {
+    return openUrl(method, uri).then((_HttpClientRequest request) {
           // Only follow redirects if initial request did.
           request.followRedirects = previous.followRedirects;
           // Allow same number of redirects.
@@ -1492,7 +1492,7 @@ class _DetachedSocket implements Socket {
 
   void destroy() => _socket.destroy();
   void add(List<int> data) => _socket.add(data);
-  Future<Socket> close() => _socket.close();
+  void close() => _socket.close();
 }