Process outstanding events before making a new HTTP client request

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 bd382bccc28d645f8faae0cee7bfd58069cb6433..42c1db9843c22ec0041a4231469a7118a70beefe 100644
--- a/sdk/lib/io/http_impl.dart
+++ b/sdk/lib/io/http_impl.dart
@@ -1883,7 +1883,11 @@ class _HttpClient implements HttpClient {
           // On error, continue with next proxy.
           .catchError(connect);
     }
-    return connect(new HttpException("No proxies given"));
+    // Make sure we go through the event loop before taking a
+    // connection from the pool. For long-running synchronous code the
+    // server might have closed the connection, so this lowers the
+    // probability of getting a connection that was already closed.
+    return new Future(() => connect(new HttpException("No proxies given")));
   }
 
   _SiteCredentials _findCredentials(Uri url, [_AuthenticationScheme scheme]) {