Generate an error for active connections when the HTTP client is shutdown

tests/standalone/io/http_server_early_client_close_test.dart

 #import("dart:io");
 #import("dart:isolate");
 
 void sendData(List<int> data, int port) {
   Socket socket = new Socket("127.0.0.1", port);
   socket.onConnect = () {
     socket.onData = () {
       Expect.fail("No data response was expected");
     };
     socket.outputStream.onNoPendingWrites = () {
@@ skipping 45 matching lines @@
 }
 
 void testEarlyClose() {
   List<EarlyCloseTest> tests = new List<EarlyCloseTest>();
   void add(Object data, String exception, {bool expectRequest: false}) {
     tests.add(new EarlyCloseTest(data, exception, expectRequest));
   }
   // The empty packet is valid.
 
   // Close while sending header
-  add("G", "Connection closed before full header was received");
-  add("GET /", "Connection closed before full header was received");
-  add("GET / HTTP/1.1", "Connection closed before full header was received");
-  add("GET / HTTP/1.1\r\n", "Connection closed before full header was received");
+  String message = "Connection closed before full request header was received";
+  add("G", message);
+  add("GET /", message);
+  add("GET / HTTP/1.1", message);
+  add("GET / HTTP/1.1\r\n", message);
 
   // Close while sending content
   add("GET / HTTP/1.1\r\nContent-Length: 100\r\n\r\n",
-      "Connection closed before full body was received",
+      "Connection closed before full request body was received",
       expectRequest: true);
   add("GET / HTTP/1.1\r\nContent-Length: 100\r\n\r\n1",
-      "Connection closed before full body was received",
+      "Connection closed before full request body was received",
       expectRequest: true);
 
 
   HttpServer server = new HttpServer();
   server.listen("127.0.0.1", 0);
   void runTest(Iterator it) {
     if (it.hasNext) {
       it.next().execute(server).then((_) => runTest(it));
     } else {
       server.close();
     }
   }
   runTest(tests.iterator());
 }
 
 void main() {
   testEarlyClose();
 }