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

tests/standalone/io/http_content_length_test.dart

Index: tests/standalone/io/http_content_length_test.dart
diff --git a/tests/standalone/io/http_content_length_test.dart b/tests/standalone/io/http_content_length_test.dart
index 917b014c1de1c632c82e5af6eedd38c345f6af35..47ef94166916fcfcc8ce7d344f40c9c0db054aab 100644
--- a/tests/standalone/io/http_content_length_test.dart
+++ b/tests/standalone/io/http_content_length_test.dart
@@ -38,10 +38,13 @@ void testNoBody(int totalConnections, bool explicitContentLength) {
       Expect.equals("0", response.headers.value('content-length'));
       Expect.equals(0, response.contentLength);
       count++;
-      if (count == totalConnections) {
-        client.shutdown();
-        server.close();
-      }
+      response.inputStream.onData = response.inputStream.read;
+      response.inputStream.onClosed = () {
+        if (count == totalConnections) {
+          client.shutdown();
+          server.close();
+        }
+      };
     };
   }
 }
@@ -82,10 +85,13 @@ void testBody(int totalConnections) {
       Expect.equals("2", response.headers.value('content-length'));
       Expect.equals(2, response.contentLength);
       count++;
-      if (count == totalConnections) {
-        client.shutdown();
-        server.close();
-      }
+      response.inputStream.onData = response.inputStream.read;
+      response.inputStream.onClosed = () {
+        if (count == totalConnections) {
+          client.shutdown();
+          server.close();
+        }
+      };
     };
   }
 }