Close servers for bin directories when precompiling executables.

sdk/lib/_internal/pub/lib/src/entrypoint.dart

Index: sdk/lib/_internal/pub/lib/src/entrypoint.dart
diff --git a/sdk/lib/_internal/pub/lib/src/entrypoint.dart b/sdk/lib/_internal/pub/lib/src/entrypoint.dart
index 16b19a59259207afabb4493ae3fd744c18a89e10..b580f49444f0e46c55768e54f5e170244d8e482b 100644
--- a/sdk/lib/_internal/pub/lib/src/entrypoint.dart
+++ b/sdk/lib/_internal/pub/lib/src/entrypoint.dart
@@ -254,7 +254,11 @@ class Entrypoint {
                 result.stderr.join('\n'));
           }
         });
-      }));
+      })).whenComplete(() {
+        // Don't return this future, since we have no need to wait for the
+        // server to fully shut down.
+        server.close();
+      });
     });
   }