Start better error reporting for sockets

runtime/bin/http_impl.dart

Index: runtime/bin/http_impl.dart
diff --git a/runtime/bin/http_impl.dart b/runtime/bin/http_impl.dart
index e5844f46de7cc15c8d15c7ed77f497abf249c037..b79a2cfcd9e0722ff12745fb1ef6e4294a6c21fb 100644
--- a/runtime/bin/http_impl.dart
+++ b/runtime/bin/http_impl.dart
@@ -509,11 +509,11 @@ class _HttpConnectionBase implements Hashable {
     if (_onDisconnectCallback != null) _onDisconnectCallback();
   }
 
-  void _onError() {
+  void _onError(Exception e) {
     // If an error occours, treat the socket as closed.
     _onClosed();
     if (_onErrorCallback != null) {
-      _onErrorCallback("Connection closed while sending data to client.");
+      _onErrorCallback("Connection closed while sending data to client ($e).");
     }
   }
 
@@ -1070,7 +1070,7 @@ class _HttpClient implements HttpClient {
         _activeSockets.add(socketConn);
         _connectionOpened(socketConn, connection);
       };
-      socket.onError = () {
+      socket.onError = (Exception e) {
         if (_onError !== null) {
           _onError(HttpStatus.NETWORK_CONNECT_TIMEOUT_ERROR);
         }