Close servers for bin directories when precompiling executables.

R=rnystrom@google.com
BUG=20482

Review URL: https://codereview.chromium.org//491103002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@39431 260f80e4-7a28-3924-810f-c04153c831b5

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();
+      });
     });
   }